CSAT 2017: every question, solved
80 questions from the official UPSC Prelims 2017 paper, in paper order. Tap an option; the answer and the reason appear instantly.
Read the passage
What climate change will undeniably do is cause or amplify events that hasten the reduction of resources. Competition over these diminishing resources would ensue in the form of political or even violent conflict. Resource-based conflicts have rarely been overt and are thus difficult to isolate. Instead they take on veneers that appear more politically palatable. Conflicts over resources like water are often cloaked in the guise of identity or ideology.
What does the above passage imply?
Answer (c) & explanation
The passage implies that environmental issues add to resource stress and political conflict (c). Step 1: it says climate change speeds up "the reduction of resources", and competition for them can turn into "political or even violent conflict". That is option (c). Step 2: option (a) says such conflicts are always political. The word "always" goes too far. Step 3: options (b) and (d) say there are no solutions or that conflicts cannot be resolved. The passage never discusses solutions at all.
Tip: when a passage describes a chain, here climate to scarcity to conflict, the right answer usually restates that chain. Reject options with "always", "no" or "cannot" unless the passage says so.
Answer as per the official UPSC answer key.
Read the passage
The man who is perpetually hesitating which of the two things he will do first, will do neither. The man who resolves, but suffers his resolution to be changed by the first counter-suggestion of a friend—who fluctuates from opinion to opinion and veers from plan to plan—can never accomplish anything. He will at best be stationary and probably retrograde in all. It is only the man who first consults wisely, then resolves firmly and then executes his purpose with inflexible perseverance, undismayed by those petty difficulties which daunt a weaker spirit—that can advance to eminence in any line.
The keynote that seems to be emerging from the passage is that
Answer (a) & explanation
The keynote is that we should first consult wisely and then decide firmly (a). Step 1: the closing line gives the order: a wise person "first consults wisely, then resolves firmly". That is option (a). Step 2: option (b), rejecting friends' advice, ignores the need to consult. Step 3: option (d), being resolute and achievement-minded, keeps the firmness but drops the consulting step. Option (c), always being broad-minded, misses the firm decision. Only (a) keeps both halves in the right order.
Tip: when the passage ends with a summary line, the keynote is usually there. Choose the option that keeps every part of it, not just one half.
Answer as per the official UPSC answer key.
Read the passage
During the summer in the Arctic Ocean, sea ice has been melting earlier and faster, and the winter freeze has been coming later. In the last three decades, the extent of summer ice has declined by about 30 per cent. The lengthening period of summer melt threatens to undermine the whole Arctic food web, atop which stand polar bears.
Which among the following is the most crucial message conveyed by the above passage?
Answer (d) & explanation
The crucial message is that climate change threatens the survival of polar bears (d). Step 1: the passage says the longer melt season "threatens to undermine the whole Arctic food web, atop which stand polar bears". So the bears' survival is at risk. Step 2: option (a) says Arctic summer is getting shorter. The passage says it is getting longer. Step 3: option (c) reverses cause and effect: the food web supports the bears, not the other way round. Option (b), moving bears to the South Pole, is never suggested.
Tip: watch for options that flip a fact (longer to shorter) or reverse a cause. These small changes are common traps.
Answer as per the official UPSC answer key.
Read the passage
Why do people prefer open defecation and not want toilets or, if they have them, only use them sometimes? Recent research has shown two critical elements : ideas of purity and pollution, and not wanting pits or septic tanks to fill because they have to be emptied. These are the issues that nobody wants to talk about, but if we want to eradicate the practice of open defecation, they have to be confronted and dealt properly.
Which among the following is the most crucial message conveyed by the above passage?
Answer (b) & explanation
The crucial message is that people must see toilet use and pit-emptying as clean, not polluting (b). Step 1: the passage says ideas of purity and pollution, and the dislike of emptying pits, "have to be confronted". So people's view of toilets must change. That is option (b). Step 2: options (a) and (c) say these ideas cannot be removed and people cannot change. That contradicts the call to act. Step 3: option (d), that people have no civic sense or privacy, is not the passage's claim.
Tip: when the author says something "has to be" done, the author believes change is possible. So options saying "cannot" go against the author. Swachh Bharat faced exactly this behaviour challenge.
Answer as per the official UPSC answer key.
Read the passage
In the last two decades, the world’s gross domestic product (GDP) has increased by 50 per cent, whereas inclusive wealth has increased by a mere 6 per cent. In recent decades, GDP-driven economic performance has only harmed inclusive wealth like human capital; and natural capital like forests, land and water. While the world’s human capital which stands at 57 per cent of total inclusive wealth grew by only 8 per cent, the natural capital which is 23 per cent of total inclusive wealth declined by 30 per cent worldwide in the last two decades.
Which of the following is the most crucial inference from the above passage?
Answer (b) & explanation
The crucial inference is that growth driven by GDP alone is neither desirable nor sustainable (b). Step 1: the passage says GDP rose about 50%, but inclusive wealth rose only 6%, and natural capital fell about 30%. So GDP growth hid a loss of real wealth. Step 2: this means GDP-only growth is not sustainable, which is option (b). Step 3: options (a) and (d) each pick one part of the argument, natural or human capital. Option (c), that world economic performance is unsatisfactory, is too vague.
Tip: inclusive wealth counts natural, human and produced capital together. A rising GDP with falling natural capital means a country is spending its savings.
Answer as per the official UPSC answer key.
Read the passage
By 2020, when the global economy is expected to run short of 56 million young people, India, with its youth surplus of 47 million, could fill the gap. It is in this context that labour reforms are often cited as the way to unlock double-digit growth in India. In 2014, India’s labour force was estimated to be about 40 per cent of the population, but 93 per cent of this force was in unorganized sector. Over the last decade, the compound annual growth rate (CAGR) of employment has slowed to 0·5 per cent, with about 14 million jobs created during last year when the labour force increased by about 15 million.
Which of the following is the most rational inference from the above passage?
Answer (b) & explanation
The rational inference is that labour reforms are needed to use India's large workforce productively (b). Step 1: the passage says about 93% of India's workforce is unorganised, and calls labour reform "the way to unlock double-digit growth". That is option (b). Step 2: option (c) says India will reach double-digit growth very soon. But the passage notes slow job growth, so that is not certain. Step 3: option (d) calls the youth skilled, which the passage never says. Option (a), population control, is not discussed.
Tip: an inference should not promise more than the passage. "Very soon" and "skilled" are added claims, so reject them. India's four labour codes, in force since 21 November 2025, are such a reform.
Answer as per the official UPSC answer key.
Read the passage
The very first lesson that should be taught to us when we are old enough to understand it, is that complete freedom from the obligation to work is unnatural, and ought to be illegal, as we can escape our share of the burden of work only by throwing it on someone else’s shoulders. Nature ordains that the human race shall perish of famine if it stops working. We cannot escape from this tyranny. The question we have to settle is how much leisure we can afford to allow ourselves.
The main idea of the passage is that
Answer (a) & explanation
The main idea is that work is essential for human beings (a). Step 1: the passage says freedom from work is "unnatural", and humanity "shall perish of famine if it stops working". So work is necessary for survival. Step 2: option (b), a balance of work and leisure, is raised only near the end, not as the main idea. Step 3: option (c) calls work a tyranny we must face. The word "tyranny" is a figure of speech in the passage, not its message. Option (d), understanding the nature of work, is too vague.
Tip: the main idea is the claim the author repeats and backs with reasons. A colourful word used once is rarely the point.
Answer as per the official UPSC answer key.
Read the passage
There is no harm in cultivating habits so long as they are not injurious. Indeed, most of us are little more than bundle of habits. Take away our habits and the residuum would hardly be worth bothering about. We could not get on without them. They simplify the mechanism of life. They enable us to do a multitude of things automatically, which, if we had to give fresh and original thought to them each time, would make existence an impossible confusion.
The author suggests that habits
Answer (c) & explanation
The author suggests that habits make it easier for us to live (c). Step 1: the passage says habits "simplify the mechanism of life" and save us from "an impossible confusion". So habits make daily life easier. That is option (c). Step 2: option (a), that habits make life difficult, is the opposite. Step 3: option (d) says habits mechanise our lives. The passage says habits work "automatically", but it means they free us, not that they make us machines. Option (b), adding precision, is not the author's point.
Tip: do not confuse a word in the passage, like "mechanism", with the option built from it. Match the meaning, not just the word.
Answer as per the official UPSC answer key.
Consider the given information and answer the item that follows.
No supporters of 'party X', who knew Z and supported his campaign strategy, agreed for the alliance with 'party Y'; but some of them had friends in 'party Y'.
With reference to the above information, which one among the following statements must be true?
Answer (b) & explanation
Option (b) must be true: at least one supporter of party Y knows some supporter of party X as a friend (b). Step 1: the information says some X supporters, who knew Z and backed his strategy, "had friends in party Y". Step 2: a friendship goes both ways. So at least one Y supporter has an X supporter as a friend. That is option (b). Step 3: options (c) and (d) say no X supporter backed Z's strategy or knew Z. Both contradict the information. Option (a) is about what Y supporters thought of the alliance, which is never given.
Tip: "must be true" needs proof from the facts. Turn the given sentence around; friendship is mutual, so the reverse also holds.
Answer as per the official UPSC answer key.
(Same information as the question above.)
With reference to the above information, consider the following statements :
- 1. Some supporters of 'party X' knew Z.
- 2. Some supporters of 'party X', who opposed Z's campaign strategy, knew Z.
- 3. No supporters of 'party X' supported Z's campaign strategy.
Which of the statements given above is/are not correct?
Answer (c) & explanation
Only statement 3 is not correct (c). Step 1: the information talks about X supporters who knew Z and supported his strategy. So some X supporters knew Z, and statement 1 is correct. Step 2: statement 3 says no X supporter backed Z's strategy. That plainly contradicts the information, so 3 is not correct. Step 3: statement 2 is about other X supporters, who opposed Z's strategy but knew him. The information neither confirms nor denies this. So it cannot be called wrong. Options (a), (b) and (d) fail.
Tip: "not correct" means proven false. A statement the facts do not mention is "unknown", not "incorrect". Keep these three groups apart: true, false and unknown.
Answer as per the official UPSC answer key.
If second and fourth Saturdays and all the Sundays are taken as only holidays for an office, what would be the minimum number of possible working days of any month of any year?
Answer (b) & explanation
The minimum is 22 working days (b). Step 1: every month has exactly two "second and fourth" Saturdays. Sundays number 4 or 5. Step 2: February in a normal year has 28 days and 4 Sundays: 28 − 4 − 2 = 22. A leap-year February with 5 Sundays: 29 − 5 − 2 = 22. Step 3: a 30-day month with 5 Sundays gives 30 − 5 − 2 = 23. A 31-day month gives at least 24. So the minimum is 22. Option (a), 23, is from a 30-day month. Options (c) and (d) would need more holidays than possible.
Tip: for "minimum in any month", test the shortest month first, February, with the most Sundays it can have.
a 30-day month with 5 Sundays gives 23. February is the shortest month.
Answer as per the official UPSC answer key.
If there is a policy that 1/3rd of a population of a community has migrated every year from one place to some other place, what is the leftover population of that community after the sixth year, if there is no further growth in the population during this period?
Answer (d) & explanation
The leftover population is 64/729 of the original (d). Step 1: each year one-third leave, so two-thirds stay. The cut applies to the population left that year, not the original. Step 2: after one year, 2/3 remains. After two years, 2/3 × 2/3 = 4/9. Keep multiplying. Step 3: after six years: (2/3)⁶ = 64 ÷ 729 = 64/729. Option (b), 32/243, is (2/3)⁵, five years. Option (a), 16/243, and option (c), 32/729, are mixed-up powers.
Tip: a fixed fraction lost each year works like compound interest in reverse. Multiply by the "staying" fraction once for each year. 2⁶ = 64 and 3⁶ = 729.
(a) and (b) are (2/3)4 and (2/3)5 written over 243. Count six years.
Answer as per the official UPSC answer key.
Four tests—Physics, Chemistry, Mathematics and Biology are to be conducted on four consecutive days, not necessarily in the same order. The Physics test is held before the test which is conducted after Biology. Chemistry is conducted exactly after two tests are held. Which is the last test held?
Answer (c) & explanation
Mathematics is the last test (c). Step 1: "Chemistry is conducted exactly after two tests" means Chemistry is on day 3. Step 2: "Physics is held before the test which is conducted after Biology." So Biology is followed by some test, and Physics comes before that test. The only way to fit this with Chemistry on day 3 is Physics on day 1 and Biology on day 2. Then Chemistry, on day 3, follows Biology, and Physics is before it. Step 3: so Mathematics is on day 4. Options (a) Physics, (b) Biology and (d) Chemistry hold days 1, 2 and 3.
Tip: fix the item with an exact position first, then fit the rest around it.
Answer as per the official UPSC answer key.
The sum of income of A and B is more than that of C and D taken together. The sum of income of A and C is the same as that of B and D taken together. Moreover, A earns half as much as the sum of the income of B and D. Whose income is the highest?
Answer (b) & explanation
B has the highest income (b). Step 1: A earns half of B + D, so B + D = 2A. Also A + C = B + D, so A + C = 2A, which gives C = A. Step 2: A + B > C + D. Since C = A, this becomes B > D. Step 3: B + D = 2A and B > D, so B is above A and D is below A. So B > A = C > D, and B is highest. Option (a) A and option (c) C are equal and in the middle. Option (d) D is the lowest.
Tip: turn each sentence into an equation and substitute step by step. Finding that two people earn the same simplifies everything else.
Answer as per the official UPSC answer key.
Consider the following :
Statement : Good voice is a natural gift but one has to keep practising to improve and excel well in the field of music.
Conclusions :
- I. Natural gifts need nurturing and care.
- II. Even though one's voice is not good, one can keep practising.
Which one of the following is correct in respect of the above statement and conclusions?
Answer (a) & explanation
Only conclusion I follows (a). Step 1: the statement says a good voice is a natural gift, but one must keep practising to excel. So even a natural gift needs work and care. That is conclusion I. Step 2: conclusion II is about people without a good voice practising. The statement says nothing about such people. So II does not follow. Step 3: so option (b), only II, and option (c), either I or II, fail. Option (d), neither, fails because I follows.
Tip: a conclusion must stay within what the statement talks about. If the statement is only about people with good voices, you cannot conclude anything about people without them.
Answer as per the official UPSC answer key.
There are three pillars X, Y and Z of different heights. Three spiders A, B and C start to climb on these pillars simultaneously. In one chance, A climbs on X by 6 cm but slips down 1 cm. B climbs on Y by 7 cm but slips down 3 cm. C climbs on Z by 6·5 cm but slips down 2 cm. If each of them requires 40 chances to reach the top of the pillars, what is the height of the shortest pillar?
Answer (b) & explanation
The shortest pillar is 163 cm (b). Step 1: in the last chance, each spider reaches the top and does not slip. So height = 39 × (net gain per chance) + one full climb. Step 2: A on X gains 6 − 1 = 5 per chance: 39 × 5 + 6 = 201 cm. B on Y gains 7 − 3 = 4: 39 × 4 + 7 = 163 cm. C on Z gains 6.5 − 2 = 4.5: 39 × 4.5 + 6.5 = 182 cm. Step 3: the shortest is 163 cm. Option (c), 182, is Z. Option (a), 161, and option (d), 210, are errors from counting slips in the 40th chance.
Tip: in climb-and-slip puzzles, the final climb has no slip. Count it separately.
40 × 4 = 160 forgets the last climb, which has no slip.
Answer as per the official UPSC answer key.
Read the passage
“Rights are certain advantageous conditions of social well-being indispensable to the true development of the citizen.”
In the light of this statement, which one of the following is the correct understanding of rights?
Answer (c) & explanation
Rights aim at both individual and social good (c). Step 1: the statement calls rights conditions "of social well-being" that are needed for "the true development of the citizen". So rights serve society and the individual at once. That is option (c). Step 2: option (a), individual good only, keeps half of the definition. Option (b), social good only, keeps the other half. Step 3: option (d), individual good without social well-being, contradicts the words "social well-being".
Tip: options with "only" often cut a two-part definition in half. When a statement names two aims, pick the option that keeps both. This view of rights is linked to the thinker Harold Laski.
Answer as per the official UPSC answer key.
15 students failed in a class of 52. After removing the names of failed students, a merit order list has been prepared in which the position of Ramesh is 22nd from the top. What is his position from the bottom?
Answer (c) & explanation
Ramesh is 16th from the bottom (c). Step 1: 15 of the 52 students failed and were removed. So the merit list has 52 − 15 = 37 names. Step 2: position from bottom = total − position from top + 1. Step 3: = 37 − 22 + 1 = 16th. Option (d), 15th, forgets to add 1. Option (a), 18th, and option (b), 17th, come from using the wrong total or adding wrongly. Check: 21 people above him, 15 below, plus him = 37.
Tip: use the "+1" rule in every rank question: top rank + bottom rank = total + 1. It works because the person is counted in both ranks.
don't use 52; the failed students are not in the list.
Answer as per the official UPSC answer key.
Consider the following :
A + B means A is the son of B.
A − B means A is the wife of B.
What does the expression P + R − Q mean?
Answer (c) & explanation
Q is P's father (c). Step 1: "A + B" means A is the son of B. So P + R means P is the son of R. Step 2: "A − B" means A is the wife of B. So R − Q means R is the wife of Q. Step 3: R is P's mother, and Q is R's husband. So Q is P's father. Option (a), Q is P's son, reverses the relation. Option (b), Q is P's wife, is wrong because Q is R's husband. Option (d) fails because (c) is clear.
Tip: decode coded relations one pair at a time, left to right. Draw a small family tree as you go; it makes the final link easy to read.
Answer as per the official UPSC answer key.
Gopal bought a cell phone and sold it to Ram at 10% profit. Then Ram wanted to sell it back to Gopal at 10% loss. What will be Gopal's position if he agreed?
Answer (c) & explanation
Gopal gains 1% (c). Step 1: suppose Gopal first paid Rs 100 for the phone. He sold it to Ram at 10% profit, for Rs 110. Step 2: Ram sells it back at 10% loss on his own price. 10% of 110 = 11, so the price is Rs 99. Step 3: Gopal now has the same phone for Rs 99 instead of Rs 100. That is Rs 1 less on every Rs 100 he first spent. That is a gain of 1%. Option (a), no loss no gain, is the trap of thinking 10% up and 10% down cancel. Options (b) and (d) do not fit.
Tip: percentages up and down use different bases, so they never simply cancel.
Counting all the cash (+110 − 100 − 99), some say Gopal is better off by ₹ 11; the official answer is (c), as printed.
Answer as per the official UPSC answer key.
Read the passage
We have hard work ahead. There is no resting for any of us till we redeem our pledge in full, till we make all the people of India what destiny intends them to be. We are citizens of a great country, on the verge of bold advance, and we have to live up to that high standard. All of us, to whatever religion we may belong, are equally the children of India with equal rights, privileges and obligations. We cannot encourage communalism or narrow-mindedness, for no nation can be great whose people are narrow in thought or action.
The challenge the author of the above passage throws to the public is to achieve
Answer (d) & explanation
The challenge is hard work, brotherhood and national unity (d). Step 1: the passage says "we have hard work ahead", that all are "equally the children of India", and that communalism must be rejected. These are hard work, brotherhood and unity. That is option (d). Step 2: option (a) mentions a high standard of living. But the passage's "high standard" is about conduct, not wealth. Step 3: options (b) and (c), privileges, destiny, adventure and economic parity, pick words that are not the author's challenge.
Tip: match each idea in an option to a phrase in the passage before choosing.
Answer as per the official UPSC answer key.
Read the passage
“The individual, according to Rousseau, puts his person and all his power in common under the supreme direction of the General Will and in our corporate capacity we receive each member as an indivisible part of the whole.”
In the light of the above passage, the nature of General Will is best described as
Answer (c) & explanation
The General Will is the collective good, distinct from private wills (c). Step 1: the passage says each person is "an indivisible part of the whole". So the General Will belongs to the community as one body. That is option (c). Step 2: option (a) calls it the sum of private wills. But Rousseau separates the General Will from the "will of all", which is just a sum of private interests. Step 3: option (b), what elected representatives say, is not mentioned. Option (d), material interests, is too narrow.
Tip: Rousseau's idea is that the General Will aims at the common good. A total of selfish wishes is not the same thing.
Answer as per the official UPSC answer key.
Read the passage
In a democratic State, where a high degree of political maturity of the people obtains, the conflict between the will of the sovereign law-making body and the organized will of the people seldom occurs.
What does the above passage imply?
Answer (d) & explanation
In a mature democracy, force is reduced to a marginal role in using sovereignty (d). Step 1: the passage says conflict between lawmakers and people "seldom occurs" in a mature democracy. So force is rarely needed. That is option (d). Step 2: option (c) says force is irrelevant. But "seldom" does not mean "never". So "irrelevant" goes too far. Step 3: options (a) and (b) say force is the main feature. That is the opposite of the passage.
Tip: match the strength of the option to the strength of the passage's words. "Seldom" fits "marginal", not "irrelevant". Small word differences decide many CSAT answers.
Answer as per the official UPSC answer key.
Read the passage
A successful democracy depends upon widespread interest and participation in politics, in which voting is an essential part. To deliberately refrain from taking such an interest, and from voting, is a kind of implied anarchy; it is to refuse one’s political responsibility while enjoying the benefits of a free political society.
This passage relates to
Answer (a) & explanation
The passage is about the duty to vote (a). Step 1: it says not voting is "to refuse one's political responsibility". Responsibility means duty. So the passage stresses voting as a duty. That is option (a). Step 2: options (b) right to vote, (c) freedom to vote and (d) right to take part in politics all talk of rights or freedoms. Step 3: these options miss the passage's stress on obligation. A right can be used or left; a duty should be done.
Tip: in India voting is a legal right, not a legal duty. But passages often argue it is a moral duty. Read the tone words, like "responsibility", to decide.
Answer as per the official UPSC answer key.
Read the passage
In a free country, the man who reaches the position of leader is usually one of outstanding character and ability. Moreover, it is usually possible to foresee that he will reach such a position, since early in life one can see his qualities of character. But this is not always true in the case of a dictator; often he reaches his position of power through chance, very often through the unhappy state of his country.
The passage seems to suggest that:
Answer (d) & explanation
The passage suggests that despair in a country sometimes leads to dictatorship (d). Step 1: it says a dictator often rises "through the unhappy state of his country". So a nation's despair can open the way to a dictator. That is option (d). Step 2: option (a) says the leader foresees his own rise. But in the passage it is others who foresee it. Step 3: option (b) says leaders are chosen only by free countries, which is too extreme. Option (c), that a leader must free his country from despair, is not the point.
Tip: history fits this idea; hard times in Germany helped Hitler rise. But always answer from the passage first.
Answer as per the official UPSC answer key.
Read the passage
The greatest blessing that technological progress has in store for mankind is not, of course, an accumulation of material possessions. The amount of these that can be effectively enjoyed by one individual in one lifetime is not great. But there is not the same narrow limit to the possibilities of the enjoyment of leisure. The gift of leisure may be abused by people who have had no experience of making use of it. Yet the creative use of leisure by a minority in societies has been the mainspring of all human progress beyond the primitive level.
With reference to the above passage, the following assumptions have been made :
- 1. People always see the leisure time as a gift and use it for acquiring more material possessions.
- 2. Use of leisure by some people to produce new and original things has been the chief source of human progress.
Which of these assumptions is/are valid?
Answer (b) & explanation
Only assumption 2 is valid (b). Step 1: the passage says "the creative use of leisure by a minority… has been the mainspring of all human progress". So some people using leisure to create new things drove progress. Assumption 2 holds. Step 2: assumption 1 says people always see leisure as a gift and use it to gain more possessions. But the passage warns leisure "may be abused", and it does not call possessions the blessing. Step 3: so assumption 1 fails, and options (a), (c) and (d) fail.
Tip: "always" in a statement is a warning sign. If the passage admits even one exception, like leisure being abused, "always" is false.
Answer as per the official UPSC answer key.
Read the passage
There is more than a modicum of truth in the assertion that “a working knowledge of ancient history is necessary to the intelligent interpretation of current events”. But the sage who uttered these words of wisdom might well have added something on the benefits of studying particularly the famous battles of history for the lessons they contain for those of us who lead or aspire to leadership. Such a study will reveal certain qualities and attributes which enabled the winners to win—and certain deficiencies which caused the losers to lose. And the student will see that the same pattern recurs consistently, again and again, throughout the centuries.
With reference to the above passage, the following assumptions have been made :
- 1. A study of the famous battles of history would help us understand the modern warfare.
- 2. Studying the history is essential for anyone who aspires to be a leader.
Which of these assumptions is/are valid?
Answer (d) & explanation
Neither assumption is valid (d). Step 1: the passage says studying famous battles teaches qualities of leadership, such as courage and judgement. It does not say they explain modern warfare. So assumption 1 fails. Step 2: the passage calls studying history beneficial for leaders. Assumption 2 says it is essential for anyone who wants to lead. "Essential" is much stronger than "beneficial". Step 3: so assumption 2 fails too, and options (a), (b) and (c) fail.
Tip: watch the gap between "helpful" and "essential", or "useful" and "necessary". CSAT setters often swap a mild word for a strong one to make a statement false.
Answer as per the official UPSC answer key.
Suppose the average weight of 9 persons is 50 kg. The average weight of the first 5 persons is 45 kg, whereas the average weight of the last 5 persons is 55 kg. Then the weight of the 5th person will be
Answer (c) & explanation
The 5th person weighs 50 kg (c). Step 1: total of all 9 = 9 × 50 = 450 kg. Step 2: total of the first 5 = 5 × 45 = 225 kg. Total of the last 5 = 5 × 55 = 275 kg. Step 3: the first five and the last five together make 10 people. But there are only 9, so the 5th person is counted twice. 225 + 275 − 450 = 50 kg. Option (a), 45 kg, is the first group's average. Options (b) and (d) are guesses between the averages.
Tip: when two groups overlap, add their totals and subtract the whole. What is left is the overlap. This trick saves time in many average questions.
Answer as per the official UPSC answer key.
In a group of six women, there are four tennis players, four postgraduates in Sociology, one postgraduate in Commerce and three bank employees. Vimala and Kamla are the bank employees while Amala and Komala are unemployed. Komala and Nirmala are among the tennis players. Amala, Kamla, Komala and Nirmala are postgraduates in Sociology of whom two are bank employees. If Shyamala is a postgraduate in Commerce, who among the following is both a tennis player and a bank employee?
Answer (c) & explanation
Nirmala is both a tennis player and a bank employee (c). Step 1: Amala, Kamla, Komala and Nirmala are the four Sociology postgraduates, and two of them are bank employees. Step 2: Amala and Komala are unemployed. So the two bank employees among them are Kamla and Nirmala. Step 3: Komala and Nirmala are tennis players. So Nirmala is both a tennis player and a bank employee. Option (a) Amala and option (b) Komala are unemployed. Option (d) Shyamala is the Commerce postgraduate, and nothing makes her both.
Tip: in group puzzles, use the "unemployed" or "not" clues to rule people out first. The right person is then the one left in both groups.
Answer as per the official UPSC answer key.
P = (40% of A) + (65% of B) and Q = (50% of A) + (50% of B), where A is greater than B. In this context, which of the following statements is correct?
Answer (d) & explanation
Nothing can be concluded with certainty (d). Step 1: P − Q = (0.40A + 0.65B) − (0.50A + 0.50B) = 0.15B − 0.10A. Step 2: the sign depends on how much bigger A is than B. If A = 1.2B, then 0.15B − 0.12B is positive, so P > Q. Step 3: if A = 2B, then 0.15B − 0.20B is negative, so P < Q. If A = 1.5B, P = Q. So options (a), (b) and (c) are each possible but not certain.
Tip: when an answer depends on values you are not given, test two very different cases. If they give different results, choose "cannot be concluded".
Answer as per the official UPSC answer key.
A watch loses 2 minutes in every 24 hours while another watch gains 2 minutes in every 24 hours. At a particular instant, the two watches showed an identical time. Which of the following statements is correct if 24-hour clock is followed?
Answer (d) & explanation
None of the statements is correct (d). Step 1: one watch loses 2 minutes a day and the other gains 2 minutes a day. So they drift apart by 4 minutes a day. Step 2: on a 24-hour clock, they show the same time again only when the gap is a full 24 hours, which is 1440 minutes. Step 3: days needed = 1440 ÷ 4 = 360 days. This is not 30, 90 or 120. So options (a), (b) and (c) are wrong. Option (b), 90 days, would be the answer only for a 6-hour gap.
Tip: on a 12-hour clock the full gap is 720 minutes; on a 24-hour clock it is 1440. Read which clock the question uses.
on a 12-hour dial the answer would be 180 days. The question says 24-hour clock, and none of the options fit either way.
Answer as per the official UPSC answer key.
In a city, 12% of households earn less than ₹ 30,000 per year, 6% households earn more than ₹ 2,00,000 per year, 22% households earn more than ₹ 1,00,000 per year and 990 households earn between ₹ 30,000 and ₹ 1,00,000 per year. How many households earn between ₹ 1,00,000 and ₹ 2,00,000 per year?
Answer (b) & explanation
240 households earn between Rs 1 lakh and Rs 2 lakh (b). Step 1: 12% earn below Rs 30,000 and 22% earn above Rs 1 lakh. So the middle group, Rs 30,000 to Rs 1 lakh, is 100 − 12 − 22 = 66%. Step 2: 66% = 990 households, so 1% = 15 households. Step 3: those above Rs 1 lakh are 22%, and those above Rs 2 lakh are 6%. So Rs 1 lakh to Rs 2 lakh = 22 − 6 = 16% = 16 × 15 = 240. Options (a), (c) and (d) do not fit.
Tip: "more than Rs 1 lakh" includes "more than Rs 2 lakh". Subtract the inner group to get the band in between.
the 6% earning over ₹ 2 lakh is inside the 22%.
Answer as per the official UPSC answer key.
A clock strikes once at 1 o'clock, twice at 2 o'clock and thrice at 3 o'clock, and so on. If it takes 12 seconds to strike at 5 o'clock, what is the time taken by it to strike at 10 o'clock?
Answer (b) & explanation
The official answer is 24 seconds (b). Step 1: the official key treats the time as shared per strike. Five strikes take 12 seconds. Step 2: ten strikes are twice five strikes, so the time doubles: 12 × 2 = 24 seconds. Step 3: strictly, a clock's time runs between strikes. Five strikes have 4 gaps, so each gap is 3 seconds, and ten strikes have 9 gaps, which would give 27 seconds. Since 27 is not an option, UPSC's key follows the simple per-strike method. Options (a), (c) and (d) do not fit either method.
Tip: if the gap method gives no matching option, fall back on simple proportion, as UPSC did here.
Counting the gaps between strikes (4 gaps take 12 s, so 9 gaps take 27 s) gives 27 s, which is not an option; the official answer is (b).
Answer as per the official UPSC answer key.
Consider the given statement and the two conclusions that follow :
Statement : Morning walk is good for health.
Conclusions :
- 1. All healthy people go for morning walk.
- 2. Morning walk is essential for maintaining good health.
What is/are the valid conclusion/conclusions?
Answer (d) & explanation
Neither conclusion is valid (d). Step 1: the statement says morning walk is good for health. Step 2: conclusion 2 says morning walk is essential for good health. "Good for" is not "essential for"; people can stay healthy through other exercise. So 2 does not follow. Step 3: conclusion 1 says all healthy people take morning walks. Healthy people may stay fit in other ways, like yoga or sport. So 1 does not follow either. Options (a), (b) and (c) fail.
Tip: "A is good for B" never means "B needs A" or "everyone with B does A". Do not reverse a statement or make it stronger than it is.
words like 'all' and 'essential' are stronger than the statement. Reject them.
Answer as per the official UPSC answer key.
There are thirteen 2-digit consecutive odd numbers. If 39 is the mean of the first five such numbers, then what is the mean of all the thirteen numbers?
Answer (a) & explanation
The mean of all thirteen numbers is 47 (a). Step 1: for evenly spaced numbers, the mean equals the middle term. The first five have mean 39, so 39 is their middle (3rd) number. The five are 35, 37, 39, 41 and 43. Step 2: the thirteen numbers start at 35 and go up by 2: 35, 37, … up to 59. Step 3: their middle term is the 7th one: 35 + 6 × 2 = 47. So the mean is 47. Options (b) 49 and (c) 51 are too high. Option (d), 45, is too low.
Tip: in any evenly spaced list, mean = middle term = (first + last) ÷ 2. Here (35 + 59) ÷ 2 = 47, which checks out.
Answer as per the official UPSC answer key.
Six boys A, B, C, D, E and F play a game of cards. Each has a pack of 10 cards. F borrows 2 cards from A and gives away 5 to C who in turn gives 3 to B while B gives 6 to D who passes on 1 to E. Then the number of cards possessed by D and E is equal to the number of cards possessed by
Answer (b) & explanation
D and E together have as many cards as B, C and F (b). Step 1: everyone starts with 10. F borrows 2 from A: A 8, F 12. F gives 5 to C: F 7, C 15. Step 2: C gives 3 to B: C 12, B 13. B gives 6 to D: B 7, D 16. D gives 1 to E: D 15, E 11. Step 3: final count: A 8, B 7, C 12, D 15, E 11, F 7. D + E = 26. B + C + F = 7 + 12 + 7 = 26. Option (a) gives 27. Option (c) gives 22. Option (d) gives 27.
Tip: track each person's count after every move in a small table. Check that the total stays 60; if not, you have made a slip.
Answer as per the official UPSC answer key.
There is a milk sample with 50% water in it. If 1/3rd of this milk is added to equal amount of pure milk, then water in the new mixture will fall down to
Answer (a) & explanation
Water in the new mixture falls to 25% (a). Step 1: take 1 litre of the sample. It has 0.5 litre water and 0.5 litre milk. Step 2: add an equal amount, 1 litre, of pure milk. Now there are 2 litres, with still only 0.5 litre of water. Step 3: water = 0.5 ÷ 2 = 25%. The "1/3rd" only says how much of the sample is used. Since an equal amount of pure milk is added, the share is always halved. Options (b), (c) and (d) do not fit.
Tip: mixing a sample with an equal amount of a pure liquid halves the share of the other part. 50% water becomes 25%, whatever the quantity.
the 1/3rd is a distraction. Equal amounts halve the water share.
Answer as per the official UPSC answer key.
There are 4 horizontal and 4 vertical lines, parallel and equidistant to one another on a board. What is the maximum number of rectangles and squares that can be formed?
Answer (c) & explanation
The maximum number of rectangles and squares is 36 (c). Step 1: any rectangle, including a square, needs 2 horizontal lines and 2 vertical lines as its sides. Step 2: ways to pick 2 lines out of 4: (1,2), (1,3), (1,4), (2,3), (2,4), (3,4). That is 6 ways. Step 3: total = horizontal choices × vertical choices = 6 × 6 = 36. Four lines each way make a 3 × 3 grid, with only 9 small squares, so options (a), (b) and (d) undercount or overcount.
Tip: with m horizontal and n vertical lines, rectangles = (m choose 2) × (n choose 2). Squares are included in this count.
Answer as per the official UPSC answer key.
A freight train left Delhi for Mumbai at an average speed of 40 km/hr. Two hours later, an express train left Delhi for Mumbai, following the freight train on a parallel track at an average speed of 60 km/hr. How far from Delhi would the express train meet the freight train?
Answer (c) & explanation
The express meets the freight train 240 km from Delhi (c). Step 1: the freight train has a 2-hour start at 40 km/hr. Its lead = 2 × 40 = 80 km. Step 2: the express is faster by 60 − 40 = 20 km/hr. This is the relative speed. The gap closes in 80 ÷ 20 = 4 hours. Step 3: in 4 hours the express covers 4 × 60 = 240 km. Check: the freight train has run 6 hours × 40 = 240 km. Option (d), 120 km, is the express's distance in 2 hours. Options (a) and (b) do not fit.
Tip: when one vehicle chases another in the same direction, subtract the speeds. The chase time = lead ÷ difference in speed.
Answer as per the official UPSC answer key.
In a test, Randhir obtained more marks than the total marks obtained by Kunal and Debu. The total marks obtained by Kunal and Shankar are more than those of Randhir. Sonal obtained more marks than Shankar. Neha obtained more marks than Randhir. Who amongst them obtained highest marks?
Answer (d) & explanation
The data are inadequate (d). Step 1: Randhir scored more than Kunal and Debu combined. Neha scored more than Randhir. Step 2: Sonal scored more than Shankar. Kunal and Shankar together beat Randhir. Step 3: nothing compares Neha with Sonal. Neha beats Randhir, and Sonal beats Shankar, but Sonal could be above or below Neha. So the top scorer cannot be found. Option (a), Randhir, is beaten by Neha. Options (b) Neha and (c) Sonal are both possible but not certain.
Tip: before naming a "highest", make sure one person is linked above everyone. Two separate chains with no link between their tops mean the data are not enough.
Answer as per the official UPSC answer key.
Read the passage
Disruption of traditional institutions, identifications and loyalties is likely to lead to ambivalent situations. It is possible that some people may renew their identification with traditional groups whereas others align themselves with new groups and symbols emergent from processes of political development. In addition, political development tends to foster group awareness of a variety of class, tribe, region, clan, language, religion, occupation and others.
Which one of the following is the best explanation of the above passage?
Answer (a) & explanation
The best explanation is that political development is not a one-way process; it involves both growth and decay (a). Step 1: the passage says some people renew old loyalties while others join new groups. So change moves in more than one direction. That is option (a). Step 2: option (c) says breaking away from old loyalties is impossible. But some people do join new groups. Step 3: option (b), that traditional societies succeed in resisting good change, is not claimed. Option (d) says old loyalties help development, which the passage does not say.
Tip: "unilinear" means moving in a single straight line. When a passage shows movement both ways, pick the option that says change is mixed.
Answer as per the official UPSC answer key.
Read the passage
There has been a significant trend worldwide towards regionalism in government, resulting in a widespread transfer of powers downwards towards regions and communities since 1990s. This process, which involves the creation of new political entities and bodies at a sub-national level and an increase in their content and powers, is known as devolution. Devolution has been characterized as being made up of three factors—political legitimacy, decentralization of authority and decentralization of resources. Political legitimacy here means a mass demand from below for the decentralization process, which is able to create a political force for it to take place. In many cases, decentralization is initiated by the upper tier of government without sufficient political mobilization for it at the grassroots level, and in such cases the decentralization process often does not fulfil its objectives.
Which among the following is the most logical, rational and critical inference that can be made from the above passage?
Answer (c) & explanation
Devolution needs democracy with free expression and active participation at the grassroots (c). Step 1: the passage says devolution needs "a mass demand from below". It adds that decentralisation imposed from the top "often does not fulfil its objectives". So people's will and participation at lower levels are key. That is option (c). Step 2: option (b), imposing devolution from the top, is exactly what the passage says fails. Step 3: option (a), powerful mass leaders, is not mentioned. Option (d), strong regionalism, is not required.
Tip: India's 73rd and 74th Amendments set up panchayats and municipalities. They work best where local people actively take part, as the passage suggests.
Answer as per the official UPSC answer key.
Read the passage
We live in digital times. The digital is not just something we use strategically and specifically to do a few tasks. Our very perception of who we are, how we connect to the world around us, and the ways in which we define our domains of life, labour and language are hugely structured by the digital technologies. The digital is everywhere and, like air, invisible. We live within digital systems, we live with intimate gadgets, we interact through digital media, and the very presence and imagination of the digital has dramatically restructured our lives. The digital, far from being a tool, is a condition and context that defines the shapes and boundaries of our understanding of the self, the society, and the structure of governance.
Which among the following is the most logical and essential message conveyed by the above passage?
Answer (b) & explanation
The message is that speaking of digital technologies is speaking of our life and living (b). Step 1: the passage calls the digital "a condition and context" that shapes self, society and governance. It is not just a tool; it is part of how we live. That is option (b). Step 2: option (a) says digital tools can solve all problems of governance. "All" goes too far. Step 3: option (c) says creativity cannot be expressed without digital media, and option (d) says digital is needed for mankind's existence. Both go well beyond the passage.
Tip: extreme words like "all", "cannot" and "existence of mankind" are signs of an overstated option.
Answer as per the official UPSC answer key.
Read the passage
The IMF has pointed out that the fast growing economies of Asia face the risk of falling into ‘middle-income trap’. It means that average incomes in these countries, which till now have been growing rapidly, will stop growing beyond a point—a point that is well short of incomes in the developed West. The IMF identifies a number of causes of middle-income trap—none of which is surprising—from infrastructure to weak institutions, to less than favourable macroeconomic conditions. But the broad, overall cause, says IMF, is a collapse in the growth of productivity.
Which among the following is the most logical, rational and critical inference that can be made from the above passage?
Answer (a) & explanation
Once a country reaches middle income, it risks falling productivity and stagnant incomes (a). Step 1: the passage says incomes stall short of Western levels because of "a collapse in the growth of productivity". That is the middle-income trap, and option (a) states it. Step 2: option (b) says the trap is a general feature of all fast-growing economies. But the passage speaks of a risk, not a rule. Step 3: option (c) says there is no hope at all for Asian economies, which is far too extreme. Option (d), Asian productivity is unsatisfactory, is too broad.
Tip: the "middle-income trap" means a country grows fast to middle income, then stalls. Higher productivity, through skills and innovation, is the way out.
Answer as per the official UPSC answer key.
Read the passage
An innovative India will be inclusive as well as technologically advanced, improving the lives of all Indians. Innovation and R&D can mitigate increases in social inequality and relieve the pressures created by rapid urbanization. The growing divergence in productivity between agriculture and knowledge-intensive manufacturing and services threatens to increase income inequality. By encouraging India’s R&D labs and universities to focus on the needs of poor people and by improving the ability of informal firms to absorb knowledge, an innovation and research agenda can counter this effect. Inclusive innovation can lower the costs of goods and services and create income-earning opportunities for the poor people.
Which among the following is the most logical and rational assumption that can be made from the above passage?
Answer (c) & explanation
The assumption is that inclusive innovation and R&D can help create a fairer society (c). Step 1: the passage says innovation "can mitigate increases in social inequality" and create income for the poor. So it can help build an egalitarian society. That is option (c). Step 2: option (a) says innovation is the only way to reduce rural-urban migration, and option (d) says urbanisation happens only with rapid growth. Both use "only". Step 3: option (b) widens India's case to every rapidly growing country, which the passage does not do.
Tip: "inclusive innovation" means low-cost ideas that reach the poor, like cheap medical devices. Reject options with "only" and "every" unless the passage says so.
Answer as per the official UPSC answer key.
Read the passage
Climate change is likely to expose a large number of people to increasing environmental risks forcing them to migrate. The international community is yet to recognize this new category of migrants. There is no consensus on the definition and status of climate refugees owing to the distinct meaning the term refugees carry under international laws. There are still gaps in understanding how climate change will work as the root cause of migration. Even if there is recognition of climate refugees, who is going to provide protection? More emphasis has been given to international migration due to climate change. But there is a need to recognize the migration of such people within the countries also so that their problems can be addressed properly.
Which of the following is the most rational inference from the above passage?
Answer (d) & explanation
The rational inference is that the link between climate change and migration is not yet properly understood (d). Step 1: the passage says: "there are still gaps in understanding how climate change will work as the root cause of migration". That is option (d). Step 2: option (c) calls climate change the most important reason for future migration. The passage never ranks it. Step 3: option (a), that the world cannot cope with climate refugees, is not stated. Option (b), stopping climate change, is a call to action the passage does not make.
Tip: when a passage admits "gaps in understanding", the safe inference is that the issue is uncertain. Options that claim certainty, like "most important", go too far.
Answer as per the official UPSC answer key.
Read the passage
Many farmers use synthetic pesticides to kill infesting insects. The consumption of pesticides in some of the developed countries is touching 3000 grams/hectare. Unfortunately, there are reports that these compounds possess inherent toxicities that endanger the health of the farm operators, consumers and the environment. Synthetic pesticides are generally persistent in environment. Entering in food chain they destroy the microbial diversity and cause ecological imbalance. Their indiscriminate use has resulted in development of resistance among insects to insecticides, upsetting of balance in nature and resurgence of treated populations. Natural pest control using the botanical pesticides is safer to the user and the environment because they break down into harmless compounds within hours or days in the presence of sunlight. Plants with pesticidal properties have been in nature for millions of years without any ill or adverse effects on the ecosystem. They are easily decomposed by many microbes common in most soils. They help in the maintenance of biological diversity of predators and the reduction of environmental contamination and human health hazards. Botanical pesticides formulated from plants are biodegradable and their use in crop protection is a practical sustainable alternative.
On the basis of the above passage, the following assumptions have been made :
- 1. Synthetic pesticides should never be used in modern agriculture.
- 2. One of the aims of sustainable agriculture is to ensure minimal ecological imbalance.
- 3. Botanical pesticides are more effective as compared to synthetic pesticides.
Which of the assumptions given above is/are correct?
Answer (b) & explanation
Only assumption 2 is correct (b). Step 1: the passage calls botanical pesticides the "sustainable alternative" because they avoid ecological imbalance. So one aim of sustainable farming is minimal imbalance. Assumption 2 holds. Step 2: assumption 1 says synthetic pesticides should never be used. But the passage faults "indiscriminate use", not all use. Step 3: assumption 3 says botanicals are more effective. The passage compares their safety, not their power. So 1 and 3 fail, and options (a), (c) and (d) fail.
Tip: separate "safer" from "more effective". Neem-based pesticides are safer for people and nature, but the passage never says they kill pests better.
Answer as per the official UPSC answer key.
Read the passage
Many farmers use synthetic pesticides to kill infesting insects. The consumption of pesticides in some of the developed countries is touching 3000 grams/hectare. Unfortunately, there are reports that these compounds possess inherent toxicities that endanger the health of the farm operators, consumers and the environment. Synthetic pesticides are generally persistent in environment. Entering in food chain they destroy the microbial diversity and cause ecological imbalance. Their indiscriminate use has resulted in development of resistance among insects to insecticides, upsetting of balance in nature and resurgence of treated populations. Natural pest control using the botanical pesticides is safer to the user and the environment because they break down into harmless compounds within hours or days in the presence of sunlight. Plants with pesticidal properties have been in nature for millions of years without any ill or adverse effects on the ecosystem. They are easily decomposed by many microbes common in most soils. They help in the maintenance of biological diversity of predators and the reduction of environmental contamination and human health hazards. Botanical pesticides formulated from plants are biodegradable and their use in crop protection is a practical sustainable alternative.
Which of the following statements is/are correct regarding biopesticides?
- 1. They are not hazardous to human health.
- 2. They are persistent in environment.
- 3. They are essential to maintain the biodiversity of any ecosystem.
Select the correct answer using the code given below.
Answer (a) & explanation
Only statement 1 is correct (a). Step 1: the passage says biopesticides reduce "human health hazards" and are "safer to the user". So statement 1 holds. Step 2: statement 2 says they are persistent in the environment. But the passage says they break down within hours or days. That is the opposite of persistent. Step 3: statement 3 calls them essential to biodiversity. The passage says they help biodiversity, not that it cannot exist without them. So options (b), (c) and (d) fail.
Tip: "persistent" means a chemical stays in the environment for a long time, like DDT. Biopesticides are valued because they are not persistent.
Answer as per the official UPSC answer key.
Certain 3-digit numbers have the following characteristics :
- 1. All the three digits are different.
- 2. The number is divisible by 7.
- 3. The number on reversing the digits is also divisible by 7.
How many such 3-digit numbers are there?
Answer (b) & explanation
There are 4 such numbers (b). Step 1: write the number as 100a + 10b + c. Number − reverse = 99(a − c). Both are divisible by 7, so 7 must divide 99(a − c). Since 7 does not divide 99, it must divide a − c. Step 2: the digits are all different, so a ≠ c. So a − c = ±7, giving end digits (1, 8), (8, 1), (2, 9), (9, 2). Step 3: test middle digits for each: 168, 861, 259 and 952 all work (168 = 7 × 24, 259 = 7 × 37). That is 4 numbers. Options (a), (c) and (d) do not fit.
Tip: number − reverse is always a multiple of 99 for 3-digit numbers. This fact unlocks many reversal puzzles.
Answer as per the official UPSC answer key.
Examine the following statements :
- 1. All colours are pleasant.
- 2. Some colours are pleasant.
- 3. No colour is pleasant.
- 4. Some colours are not pleasant.
Given that statement 4 is true, what can be definitely concluded?
Answer (d) & explanation
Statement 1 is definitely false (d). Step 1: statement 4 says "some colours are not pleasant". Step 2: this is the exact opposite of statement 1, "all colours are pleasant". If some colours are not pleasant, then not all are. So 1 is false. Step 3: statement 2, "some colours are pleasant", could be true or false. Statement 3, "no colour is pleasant", could also be true or false. So options (a), (b) and (c) are not certain.
Tip: learn the opposite pairs: "all are" against "some are not", and "none are" against "some are". If one of a pair is true, the other is false. Other pairs tell you nothing for sure.
Answer as per the official UPSC answer key.
How many numbers are there between 99 and 1000 such that the digit 8 occupies the units place?
Answer (c) & explanation
There are 90 such numbers (c). Step 1: numbers between 99 and 1000 are the three-digit numbers, 100 to 999. Step 2: the units digit is fixed as 8. The hundreds digit can be 1 to 9, which is 9 ways. The tens digit can be 0 to 9, which is 10 ways. Step 3: total = 9 × 10 = 90. These are 108, 118, … up to 998. Option (b), 80, wrongly leaves out tens digit 0 or 8. Option (a), 64, and option (d), 104, do not fit.
Tip: in digit-counting questions, fill each place separately and multiply the choices. Remember the first digit cannot be 0, but other places can.
Answer as per the official UPSC answer key.
If for a sample data Mean < Median < Mode then the distribution is
Answer (d) & explanation
The distribution is skewed to the left (d). Step 1: in a balanced, symmetric set, the mean, median and mode are all equal. So option (a) is out. Step 2: a few very small values pull the mean down the most, then the median a little. The mode stays at the peak. Step 3: so Mean < Median < Mode means a long tail on the small, left side. That is left skew, also called negative skew. Option (b), skewed to the right, would give Mean > Median > Mode. Option (c) is not a real category here.
Tip: the mean always moves towards the long tail. If the mean is the smallest of the three, the tail is on the left.
Answer as per the official UPSC answer key.
The age of Mr. X last year was the square of a number and it would be the cube of a number next year. What is the least number of years he must wait for his age to become the cube of a number again?
Answer (b) & explanation
He must wait 38 years (b). Step 1: his age last year was a square, and next year will be a cube. These two ages are 2 years apart. Look for a square and a cube that differ by 2: 25 and 27. Step 2: so last year he was 25, next year he will be 27, and now he is 26. Step 3: the next cube after 27 is 64. He must wait 64 − 26 = 38 years. Option (a), 42, does not fit. Option (c), 25, and option (d), 16, are squares from the puzzle, not the wait.
Tip: learn small squares and cubes by heart: cubes are 1, 8, 27, 64, 125. Checking pairs from such lists solves these puzzles fast.
64 – 27 = 37 counts from next year, not from now.
Answer as per the official UPSC answer key.
P works thrice as fast as Q, whereas P and Q together can work four times as fast as R. If P, Q and R together work on a job, in what ratio should they share the earnings?
Answer (a) & explanation
They should share in the ratio 3 : 1 : 1 (a). Step 1: P works three times as fast as Q. Take Q's rate as 1, so P's rate is 3. Step 2: P and Q together work four times as fast as R. P + Q = 3 + 1 = 4, so 4 = 4 × R, which gives R = 1. Step 3: earnings are shared by the amount of work done, which follows the rates. So P : Q : R = 3 : 1 : 1. Option (d), 3 : 1 : 4, treats R as 4. Options (b) and (c) do not fit.
Tip: when people work for the same time, share pay in the ratio of their speeds. Set the slowest person's speed as 1 to keep numbers simple.
Answer as per the official UPSC answer key.
Consider the following relationships among members of a family of six persons A, B, C, D, E and F :
- 1. The number of males equals that of females.
- 2. A and E are sons of F.
- 3. D is the mother of two, one boy and one girl.
- 4. B is the son of A.
- 5. There is only one married couple in the family at present.
Which one of the following inferences can be drawn from the above?
Answer (b) & explanation
A is the husband of D (b). Step 1: A and E are sons, and B is a son. So the males are A, E and B. Equal numbers means C, D and F are female. Step 2: A and E are F's sons, so F is their mother. D is the mother of one boy and one girl. D's son cannot be A or E, who are F's sons, so D's son is B. B is A's son, so D is A's wife. Step 3: C is their daughter. Since there is only one married couple, F is a widowed grandmother. Option (a) is wrong because A is male. Option (c) is wrong because E and F are not D's children. Option (d) has no support.
Tip: start with gender, then link parents and children.
Answer as per the official UPSC answer key.
A bag contains 20 balls. 8 balls are green, 7 are white and 5 are red. What is the minimum number of balls that must be picked up from the bag blindfolded (without replacing any of it) to be assured of picking at least one ball of each colour?
Answer (b) & explanation
You must pick 16 balls (b). Step 1: think of the worst case: the balls come out in the most unlucky order. Step 2: the unluckiest order gives all the balls of the two largest colours first: all 8 green and all 7 white. That is 15 balls with no red yet. Step 3: the 16th ball must be red, since only red balls are left. So 16 balls guarantee at least one of each colour. Option (a), 17, is more than needed. Option (c), 13, and option (d), 11, could still miss a colour.
Tip: for "to be sure" questions, assume the worst luck. Take all of the biggest groups first, then add one more ball.
Answer as per the official UPSC answer key.
If 2 boys and 2 girls are to be arranged in a row so that the girls are not next to each other, how many possible arrangements are there?
Answer (c) & explanation
There are 12 arrangements (c). Step 1: four different children can stand in 4 × 3 × 2 × 1 = 24 orders. Step 2: count the orders with the girls together. Tie the 2 girls into one block. Now there are 3 items, which can be arranged in 3 × 2 × 1 = 6 ways. The girls can swap inside the block, so × 2 = 12. Step 3: girls apart = 24 − 12 = 12. Option (d), 24, counts all orders. Option (b), 6, and option (a), 3, undercount.
Tip: for "not next to each other", count all orders and subtract those where they are together. Treating a pair as one block makes the "together" count easy.
Answer as per the official UPSC answer key.
The outer surface of a 4 cm × 4 cm × 4 cm cube is painted completely in red. It is sliced parallel to the faces to yield sixty four 1 cm × 1 cm × 1 cm small cubes. How many small cubes do not have painted faces?
Answer (a) & explanation
8 small cubes have no painted face (a). Step 1: the 4 × 4 × 4 cube is cut into 64 small cubes. Only the outer layer is painted. Step 2: the unpainted cubes form an inner block. Remove one layer from each side: 4 − 2 = 2 cubes along each edge. Step 3: the inner block is 2 × 2 × 2 = 8 cubes. Option (c), 24, is the number with exactly one painted face. Option (b), 16, and option (d), 36, do not fit.
Tip: for an n × n × n painted cube, unpainted = (n − 2)³, one face = 6(n − 2)², two faces = 12(n − 2), and three faces = 8. Learn these four formulas.
Answer as per the official UPSC answer key.
Consider the following :
A, B, C, D, E, F, G and H are standing in a row facing North.
B is not neighbour of G.
F is to the immediate right of G and neighbour of E.
G is not at the extreme end.
A is sixth to the left of E.
H is sixth to the right of C.
Which one of the following is correct in respect of the above?
Answer (c) & explanation
G is to the immediate right of D (c). Step 1: A is sixth to the left of E, and H is sixth to the right of C. In a row of 8, these pairs must take places 1–7 or 2–8. So A and C take places 1 and 2, and E and H take 7 and 8. Step 2: G, F, E sit together in that order. E must be 7, so F = 6 and G = 5. Then H = 8, A = 1 and C = 2. Step 3: B is not next to G, so B = 3 and D = 4. The row is A C B D G F E H. G is right of D. Options (a), (b) and (d) do not match this row.
Tip: place the "sixth to the left" pairs first; they leave few options.
Answer as per the official UPSC answer key.
In a certain code, '256' means 'red colour chalk', '589' means 'green colour flower' and '254' means 'white colour chalk'. The digit in the code that indicates 'white' is
Answer (b) & explanation
The digit for 'white' is 4 (b). Step 1: compare '256' = 'red colour chalk' with '254' = 'white colour chalk'. Step 2: both share the words colour and chalk, and both share the digits 2 and 5. Step 3: the only change is red to white, and 6 to 4. So white = 4. Option (c), 5, is shared by all three codes, so it means 'colour'. Option (a), 2, is shared by the chalk codes, so it means 'chalk'. Option (d), 8, belongs to 'green' or 'flower'.
Tip: in word-code questions, compare two codes that differ in only one word. The digit that changes is the code for that word.
Answer as per the official UPSC answer key.
Read the passage
An air quality index (AQI) is a way to combine measurements of multiple air pollutants into a single number or rating. This index is ideally kept constantly updated and available in different places. The AQI is most useful when lots of pollution data are being gathered and when pollution levels are normally, but not always, low. In such cases, if pollution levels spike for a few days, the public can quickly take preventive action (like staying indoors) in response to an air quality warning. Unfortunately, that is not urban India. Pollution levels in many large Indian cities are so high that they remain well above any health or regulatory standard for large part of the year. If our index stays in the ‘Red/Dangerous’ region day after day, there is not much any one can do, other than getting used to ignoring it.
Which among the following is the most logical and rational inference that can be made from the above passage?
Answer (c) & explanation
The inference is that the air quality index is not helpful to residents of many large cities (c). Step 1: the passage says an index stuck in 'Red' leaves residents nothing to do "other than getting used to ignoring it". So the index is not helping them. That is option (c). Step 2: option (b) says there is absolutely no need for indices anywhere. That goes beyond the large-city point. Step 3: option (a) blames governments, which the passage does not do. Option (d), more awareness in every city, is not the point.
Tip: India's AQI has six bands, from Good to Severe. The passage's point is that a warning that never changes stops being useful.
Answer as per the official UPSC answer key.
Read the passage
Productive jobs are vital for growth and a good job is the best form of inclusion. More than half of our population depends on agriculture, but the experience of other countries suggests that the number of people dependent on agriculture will have to shrink if per capita incomes in agriculture are to go up substantially. While industry is creating jobs, too many such jobs are low-productivity non-contractual jobs in the unorganized sector, offering low incomes, little protection, and no benefits. Service jobs are relatively of high productivity, but employment growth in services has been slow in recent years.
Which among the following is the most logical and rational inference that can be made from the above passage?
Answer (c) & explanation
We must create productive jobs outside agriculture while also raising farm productivity (c). Step 1: the passage says fewer people must depend on farming for farm incomes to rise. Industry and services both need productive jobs. So we need jobs outside farming and better farming. That is option (c). Step 2: option (a) covers services only, and leaves out industry. Step 3: option (b) says simply shift farm workers, ignoring farm productivity. Option (d) brings in hybrid and GM crops, which the passage does not discuss.
Tip: in India, close to half of workers are in agriculture, but it produces under a fifth of GDP. That is why moving workers to productive jobs matters.
Answer as per the official UPSC answer key.
Read the passage
A landscape-scale approach to land use can encourage greater biodiversity outside protected areas. During hurricane ‘Mitch’ in 1998, farms using ecoagricultural practices suffered 58 per cent, 70 per cent and 99 per cent less damage in Honduras, Nicaragua and Guatemala, respectively, than farms using conventional techniques. In Costa Rica, vegetative windbreaks and fencerows boosted farmers’ income from pasture and coffee while also increasing bird diversity. Bee pollination is more effective when agricultural fields are closer to natural or seminatural habitat, a finding that matters because 87 per cent of the world’s 107 leading crops depend on animal pollinators. In Costa Rica, Nicaragua and Colombia silvopastoral systems that integrate trees with pastureland are improving the sustainability of cattle production, and diversifying and increasing farmers’ income.
Which among the following is the most logical and rational inference that can be made from the above passage?
Answer (a) & explanation
Farming that boosts biodiversity can often raise output and reduce disaster risk (a). Step 1: the passage says ecofarms suffered far less hurricane damage, and windbreaks and pollinators raised income. So such practices help output and resilience. That is option (a). Step 2: option (b) says replace ecoagriculture with conventional farming. That reverses the lesson. Step 3: option (c) is about protected areas, but the approach works outside them, so (c) misreads it. Option (d) says yields will be very high, which is overstated.
Tip: ecoagriculture means farming that also protects nature, like agroforestry. Watch for options that flip the passage's lesson.
Answer as per the official UPSC answer key.
Read the passage
The medium term challenge for Indian manufacturing is to move from lower to higher tech sectors, from lower to higher value-added sectors, and from lower to higher productivity sectors. Medium tech industries are primarily capital intensive and resource processing; and high tech industries are mainly capital and technology intensive. In order to push the share of manufacturing in overall GDP to the projected 25 per cent, Indian manufacturing needs to capture the global market in sectors showing a rising trend in demand. These sectors are largely high technology and capital intensive.
Which among the following is the most logical and rational inference that can be made from the above passage?
Answer (c) & explanation
India should raise public investment and encourage private investment in R&D, technology and skills (c). Step 1: the passage says sectors with rising global demand are "high technology and capital intensive". To move into them, India needs investment in research, technology and skills. That is option (c). Step 2: option (d) says India already has a big share in these sectors. That contradicts the passage's line that India "needs to capture" it. Step 3: option (b) says such industries are not possible in India, which is defeatist. Option (a) gets the facts wrong.
Tip: a good inference points to the step that fills the gap the passage names. Here the gap is technology and capital.
Answer as per the official UPSC answer key.
Read the passage
Over the last decade, Indian agriculture has become more robust with record production of food grains and oilseeds. Increased procurement, consequently, has added huge stocks of food grains in the granaries. India is one of the world’s top producers of rice, wheat, milk, fruits and vegetables, India is still home to a quarter of all undernourished people in the world. On an average, almost half of the total expenditure of nearly half of the households is on food.
Which among the following is the most logical corollary to the above passage?
Answer (a) & explanation
Making the farm-to-fork value chain more efficient is needed to reduce poverty and malnutrition (a). Step 1: the passage notes record harvests and full granaries, yet India has about a quarter of the world's undernourished. So food is grown but not reaching people. Better supply chains are the fix. That is option (a). Step 2: option (b) says higher productivity will automatically end hunger. But output is already high, so that fails. Step 3: option (c) says no further productivity rise is needed, which is not the point. Option (d) relies on more welfare funds, which the passage does not discuss.
Tip: food security means availability, access and use. High production alone covers only the first.
Answer as per the official UPSC answer key.
Read the passage
The States are like pearls and the Centre is the thread which turns them into a necklace; if the thread snaps, the pearls are scattered.
Which one of the following views corroborates the above statement?
Answer (b) & explanation
The view that a strong Centre binds the nation together corroborates the statement (b). Step 1: the statement compares the Centre to the thread that holds pearls in a necklace. If the thread snaps, the pearls scatter. So the Centre keeps the nation united. That is option (b). Step 2: option (a) adds strong States, which the image does not mention. Step 3: options (c) and (d) speak of State autonomy, which the image also does not discuss. Option (c) even suggests the Centre is a hindrance, the opposite view.
Tip: when a statement uses an image, decode the image first. Thread = Centre, pearls = States, scattering = breakup. Then pick the option that matches.
Answer as per the official UPSC answer key.
Read the passage
Really I think that the poorest he that is in England has a life to live, as the greatest he, and therefore truly, I think it is clear that every man that is to live under a government ought first by his own consent to put himself under the government, and I do think that the poorest man in England is not at all bound in a strict sense to that government that he has not had a voice to put himself under.
The above statement argues for
Answer (b) & explanation
The statement argues for rule by the consent of the governed (b). Step 1: it says every man should live under a government only "by his own consent". That is government by consent. Option (b) states it. Step 2: the statement mentions "the poorest man" to show that even he has equal standing. It does not ask for rule of the poor (c). Step 3: options (a) equal wealth and (d) taking property from the rich are about money, which the statement does not discuss.
Tip: this idea comes from the Putney Debates in 17th-century England. "Consent of the governed" is the base of modern democracy, where people elect their rulers.
Answer as per the official UPSC answer key.
The average rainfall in a city for the first four days was recorded to be 0·40 inch. The rainfall on the last two days was in the ratio of 4 : 3. The average of six days was 0·50 inch. What was the rainfall on the fifth day?
Answer (c) & explanation
Rainfall on the fifth day was 0.80 inch (c). Step 1: total over six days = 6 × 0.50 = 3.00 inches. Total over the first four days = 4 × 0.40 = 1.60 inches. Step 2: so the last two days had 3.00 − 1.60 = 1.40 inches. Step 3: these are in the ratio 4 : 3. 1.40 ÷ 7 = 0.20, so the fifth day = 4 × 0.20 = 0.80 inch and the sixth = 0.60 inch. Option (a), 0.60, is the sixth day. Options (b) and (d) do not fit.
Tip: in average questions, turn every average into a total first. Then subtract to find the missing part, and split it by the ratio.
Answer as per the official UPSC answer key.
A, B, C, D, E, F and G are Lecturers from different cities—Hyderabad, Delhi, Shillong, Kanpur, Chennai, Mumbai and Srinagar (not necessarily in the same order) who participated in a conference. Each one of them is specialized in a different subject, viz., Economics, Commerce, History, Sociology, Geography, Mathematics and Statistics (not necessarily in the same order). Further
- 1. Lecturer from Kanpur is specialized in Geography
- 2. Lecturer D is from Shillong
- 3. Lecturer C from Delhi is specialized in Sociology
- 4. Lecturer B is specialized in neither History nor Mathematics
- 5. Lecturer A who is specialized in Economics does not belong to Hyderabad
- 6. Lecturer F who is specialized in Commerce belongs to Srinagar
- 7. Lecturer G who is specialized in Statistics belongs to Chennai
Who is specialized in Geography?
Answer (a) & explanation
B is specialised in Geography (a). Step 1: clues 3, 5, 6 and 7 fix four subjects: C has Sociology, A Economics, F Commerce and G Statistics. Step 2: the subjects left are History, Geography and Mathematics, for B, D and E. Step 3: clue 4 says B takes neither History nor Mathematics. So B takes Geography, and by clue 1 B is from Kanpur. Option (b) D and option (c) E share History and Mathematics. Option (d) fails because B is fixed.
Tip: in grid puzzles, first fill everything the clues state directly. Then use the "neither… nor" clue on the few gaps left. It usually settles one person at once.
Answer as per the official UPSC answer key.
(Same information as the question above.)
To which city does the Lecturer specialized in Economics belong?
Answer (b) & explanation
The Economics lecturer is from Mumbai (b). Step 1: list the cities already fixed: C is from Delhi, D Shillong, F Srinagar and G Chennai. B teaches Geography, so B is from Kanpur. Step 2: that leaves Hyderabad and Mumbai for A and E. Step 3: A teaches Economics and is not from Hyderabad (clue 5). So A is from Mumbai. Option (a), Hyderabad, is ruled out by clue 5. Option (c) is wrong because one of the two must fit. Option (d) fails because the answer is clear.
Tip: when two people share two places, one "not" clue settles both. Keep track of the cities still free as you go.
Answer as per the official UPSC answer key.
(Same information as the question above.)
Who of the following belongs to Hyderabad?
Answer (b) & explanation
E belongs to Hyderabad (b). Step 1: from the earlier steps, C is from Delhi, D Shillong, F Srinagar, G Chennai and B Kanpur. Step 2: A, the Economics lecturer, is from Mumbai, because A is not from Hyderabad. Step 3: the only city left is Hyderabad, and the only person left is E. Option (a) B is from Kanpur. Option (c) is wrong because E fits. Option (d) fails because the data settle it.
Tip: linked questions in a set usually build on each other. Once you have solved the grid for one question, the next answers follow quickly. Keep your table on the page and do not solve it again.
Answer as per the official UPSC answer key.
In a school, there are five teachers A, B, C, D and E. A and B teach Hindi and English. C and B teach English and Geography. D and A teach Mathematics and Hindi. E and B teach History and French. Who teaches maximum number of subjects?
Answer (b) & explanation
B teaches the most subjects (b). Step 1: list each teacher's subjects. B appears in three pairs: Hindi and English (with A), English and Geography (with C), and History and French (with E). Step 2: so B teaches Hindi, English, Geography, History and French. That is 5 subjects. Step 3: A teaches Hindi, English and Mathematics, which is 3. D teaches Mathematics and Hindi, which is 2. E teaches History and French, which is 2. C teaches English and Geography. So option (b) is right.
Tip: write each name once and list all the subjects linked to it, without repeats. The person who appears in the most pairs usually has the most subjects.
Answer as per the official UPSC answer key.
A 2-digit number is reversed. The larger of the two numbers is divided by the smaller one. What is the largest possible remainder?
Answer (d) & explanation
The largest possible remainder is 45 (d). Step 1: when the quotient is 1, the remainder is just the difference of the two numbers. That difference is always 9 × (difference of the digits). Step 2: to make the difference large while the quotient stays 1, the bigger number must be less than twice the smaller. Take digits 9 and 4: 94 ÷ 49 = 1, remainder 45. Step 3: try 95 and 59: 95 ÷ 59 = 1, remainder 36. Bigger digit gaps make the quotient 2 or more and the remainder smaller. Options (a), (b) and (c) are possible remainders but not the largest.
Tip: test the highest option first. If it works and nothing beats it, you are done.
Answer as per the official UPSC answer key.
The monthly incomes of X and Y are in the ratio of 4 : 3 and their monthly expenses are in the ratio of 3 : 2. However, each saves ₹ 6,000 per month. What is their total monthly income?
Answer (b) & explanation
Their total monthly income is Rs 42,000 (b). Step 1: test the options. Split the total income in the ratio 4 : 3, subtract Rs 6,000 savings from each, and check whether expenses come out as 3 : 2. Step 2: option (b): incomes Rs 24,000 and Rs 18,000. Expenses Rs 18,000 and Rs 12,000. 18 : 12 = 3 : 2. It works. Step 3: option (a), Rs 28,000: incomes 16,000 and 12,000, expenses 10,000 and 6,000 = 5 : 3. It fails. Options (c) and (d) also fail the expense ratio.
Tip: algebra works too: 4x − 6000 : 3x − 6000 = 3 : 2 gives x = 6000. But testing options is often faster in CSAT.
Answer as per the official UPSC answer key.
Two walls and a ceiling of a room meet at right angles at a point P. A fly is in the air 1 m from one wall, 8 m from the other wall and 9 m from the point P. How many meters is the fly from the ceiling?
Answer (a) & explanation
The fly is 4 m from the ceiling (a). Step 1: put point P at the corner where the two walls and the ceiling meet. The fly's distances from the two walls and the ceiling act like three coordinates: 1, 8 and h. Step 2: the straight distance from P is found by a 3-D Pythagoras rule: 1² + 8² + h² = 9². Step 3: 1 + 64 + h² = 81, so h² = 16 and h = 4 m. Option (b), 6, and options (c) and (d) do not fit the equation.
Tip: in a box-shaped corner, distance from the corner = √(x² + y² + z²). It is just Pythagoras used twice. This idea also gives the diagonal of a room.
Answer as per the official UPSC answer key.
Directions for the following 3 (three) items : Consider the given information and answer the three items that follow.
Eight railway stations A, B, C, D, E, F, G and H are connected either by two-way passages or one-way passages. One-way passages are from C to A, E to G, B to F, D to H, G to C, E to C and H to G. Two-way passages are between A and E, G and B, F and D, and E and D.
While travelling from C to H, which one of the following stations must be passed through?
Answer (b) & explanation
Every route from C to H must pass through E (b). Step 1: look at C's exits. The only passage out of C is the one-way passage C to A. Step 2: from A, the only passage out is the two-way passage A to E. Step 3: so every trip from C to H starts C → A → E, and then goes on to H, for example through D. Option (a), G, is not needed. Option (c), D, is used in the usual route, but the question asks what must be passed, and E comes first with no choice. Option (d), F, is not needed.
Tip: draw the stations as dots and the passages as arrows. A station with only one way out decides the route.
D must also be passed (H can be reached only from D), so (c) looks right too; the official answer is (b), as printed.
Answer as per the official UPSC answer key.
(Same information as the question above.)
In how many different ways can a train travel from F to A without passing through any station more than once?
Answer (d) & explanation
There are 4 ways from F to A (d). Step 1: from F, the only way out is the two-way passage to D. B to F is one-way into F. Step 2: from D, a train can go to E or to H. Step 3: list the routes without repeating stations: F–D–E–A, F–D–E–C–A, F–D–E–G–C–A and F–D–H–G–C–A. That is 4 routes. Options (a), (b) and (c) undercount.
Tip: in route counting, branch at each station and follow every path to the end. Strike out paths that repeat a station or go the wrong way on a one-way passage. A neat tree diagram stops you missing any route.
Answer as per the official UPSC answer key.
(Same information as the question above.)
If the route between G and C is closed, which one of the following stations need not be passed through while travelling from H to C?
Answer (c) & explanation
Station A need not be passed (c). Step 1: with the G to C passage closed, find a way from H to C. From H, the only way out is the one-way passage H to G. Step 2: from G, the only way out now is G to B (two-way). From B: one-way B to F. From F: F to D. From D: D to E. From E: one-way E to C. Step 3: the only route is H → G → B → F → D → E → C. Station A is not on it. Options (a) E, (b) D and (d) B are all on the route.
Tip: when a passage is closed, re-draw just that part of the map. Then trace the only path left; stations off it are the answer.
Answer as per the official UPSC answer key.
There are certain 2-digit numbers. The difference between the number and the one obtained on reversing it is always 27. How many such maximum 2-digit numbers are there?
Answer (d) & explanation
None of the options is right (d). Step 1: number − reverse = 9 × (difference of the digits). For a difference of 27, the digits must differ by 3. Step 2: numbers where the tens digit is 3 more than the units digit: 41, 52, 63, 74, 85 and 96. That is 6. Their reverses (14, 25, 36, 47, 58, 69) also differ by 27, if we allow the difference either way, giving 12. Step 3: 30 has reverse 03, which is not a 2-digit number. So the count is 6 or 12, never 3, 4 or 5. Options (a), (b) and (c) fail.
Tip: learn that any 2-digit number minus its reverse is a multiple of 9.
Answer as per the official UPSC answer key.
What is the total number of digits printed, if a book containing 150 pages is to be numbered from 1 to 150?
Answer (b) & explanation
The total number of digits is 342 (b). Step 1: pages 1 to 9 use 1 digit each: 9 digits. Step 2: pages 10 to 99 are 90 pages with 2 digits each: 180 digits. Step 3: pages 100 to 150 are 51 pages with 3 digits each: 153 digits. Total = 9 + 180 + 153 = 342. Option (a), 262, and option (c), 360, are calculation slips. Option (d), 450, assumes 3 digits on every page.
Tip: split page numbers into 1-digit, 2-digit and 3-digit groups. Count pages in each group carefully: from 100 to 150 there are 51 pages, not 50.
Answer as per the official UPSC answer key.
All years by topic
Every question from 2011 to 2026, grouped by syllabus topic, with year-wise trends.