CSAT (Paper II): previous-year questions
1280 real UPSC Prelims questions (2011–2026) with the official answer and a clear explanation. 400 of them came in the last five papers.
How often UPSC asks this
Questions per year, counted from the official papers.
Subtopics
Arrangements, ranking, ordering and puzzles
142 questions
Clocks and calendars
5 questions
Coding-decoding, series, patterns, cubes, dice and visual reasoning
110 questions
Communication, interpersonal skills and decision-making
10 questions
Counting, permutations, combinations and probability
1 questions
Directions, blood relations and Venn diagrams
60 questions
General English: grammar, vocabulary and comprehension
20 questions
General Hindi: grammar, vocabulary, dialects and comprehension
25 questions
Geometry and mensuration
26 questions
Number system and basic algebra (divisibility, HCF/LCM, remainders, digits, equations)
196 questions
Percentages, profit and loss, discount, simple and compound interest
47 questions
Ratio, proportion, averages, mixtures and alligation
47 questions
Syllogisms, statements and conclusions, assumptions and arguments
89 questions
Time and work; pipes and cisterns
2 questions
Time, speed and distance; trains, boats and streams; races
48 questions
Attempt the questions
Newest papers first. Tap an option; the answer and the reason appear instantly.
In a question paper there are five questions to be attempted and answer to each question has two choices — True (T) or False (F). It is given that no two candidates have given the answers to the five questions in an identical sequence. For this to happen, the maximum number of candidates is :
Answer (d) & explanation
At most 32 candidates (d). Step 1: each question has 2 possible answers, True or False. Step 2: for five questions, the number of different answer patterns is 2 × 2 × 2 × 2 × 2 = 32. Step 3: if no two candidates may have the same pattern, there can be at most 32 candidates. Option (a), 10, is 2 × 5, a common mistake of multiplying instead of raising to the power. Options (b) 18 and (c) 26 do not fit.
Tip: when each of n choices has k options, the number of combinations is k multiplied by itself n times. For yes/no questions that is 2, 4, 8, 16, 32 and so on.
Answer as per the official UPSC answer key.
Four-digit numbers are to be formed using the digits 1, 2, 3 and 4; and none of these four digits are repeated in any manner. Further,
- 1. 2 and 3 are not to immediately follow each other
- 2. 1 is not to be immediately followed by 3
- 3. 4 is not to appear at the last place
- 4. 1 is not to appear at the first place
How many different numbers can be formed ?
Answer (a) & explanation
Six numbers can be formed (a). Step 1: the rules are: 2 and 3 are not next to each other, 1 is not directly before 3, 4 is not last, and 1 is not first. So each number starts with 2, 3 or 4. Step 2: test each arrangement. Numbers starting with 2: 2143, 2431. Starting with 3: 3142, 3412, 3421. Starting with 4: 4312. Step 3: every other order breaks a rule, for example 2134 ends in 4, and 4213 has 1 before 3. That is 6 numbers. Options (b), (c) and (d) do not fit.
Tip: when there are only 24 orders, list them in a fixed order by first digit. A neat list stops you missing or repeating any.
Answer as per the official UPSC answer key.
(Same information as the question above.)
Who of the following is definitely a man ?
Answer (c) & explanation
Q is definitely a man (c). Step 1: the puzzle says Q is "the brother of P". A brother is male, so Q is certainly a man. Step 2: T is also described as a man. But T is not one of the options, apart from "None of the above", which is wrong because Q qualifies. Step 3: the genders of P and S are never given. P could be Q's brother or sister, and S could be either. So options (a) and (b) are not certain. Option (d) fails because Q is a man.
Tip: "definitely" means the facts must prove it. Do not assume gender from names, jobs or seating; only words like brother, wife or "a man" count.
Answer as per the official UPSC answer key.
The sum of the ages of 5 members comprising a family, 3 years ago was 80 years. The average age of the family today is the same as it was 3 years ago, because of an addition of a baby during the intervening period. How old is the baby?
Answer (b) & explanation
The baby is 1 year old (b). Step 1: three years ago, the 5 members' ages added to 80. So the average was 80 ÷ 5 = 16. Step 2: today each of the five is 3 years older. Their total = 80 + 5 × 3 = 95. Step 3: with the baby there are 6 members, and the average is still 16. So the total = 6 × 16 = 96. Baby = 96 − 95 = 1 year. Option (a), 6 months, and options (c) and (d) do not fit.
Tip: in age-average questions, work with totals, not averages. Every year adds 1 year to each person, so a group of n people gains n years in total each year.
Answer as per the official UPSC answer key.
Anita's mathematics test had 70 problems carrying equal marks i.e., 10 arithmetic, 30 algebra and 30 geometry. Although she answered 70% of the arithmetic, 40% of the algebra and 60% of the geometry problems correctly, she did not pass the test because she got less than 60% marks. The number of more questions she would have to answer correctly to earn a 60% passing marks is :
Answer (b) & explanation
She needed 5 more correct answers (b). Step 1: count her correct answers. Arithmetic: 70% of 10 = 7. Algebra: 40% of 30 = 12. Geometry: 60% of 30 = 18. Total = 37. Step 2: passing needs 60% of 70 = 42 correct answers. Step 3: she needs 42 − 37 = 5 more. Option (a), 1, is too few. Option (c), 7, and option (d), 9, are too many. Since all questions carry equal marks, you can count questions instead of marks.
Tip: work out each part separately and then add. Do not average the percentages (70, 40 and 60), because each section has a different number of questions.
averaging the three percentages ignores the different section sizes.
Answer as per the official UPSC answer key.
If R and S are different integers both divisible by 5, then which of the following is not necessarily true?
Answer (b) & explanation
"R + S is divisible by 10" is not always true (b). Step 1: R and S are multiples of 5, so write R = 5a and S = 5b. Step 2: R − S = 5(a − b), divisible by 5. R × S = 25ab, divisible by 25. R² + S² = 25(a² + b²), divisible by 5. So options (a), (c) and (d) always hold. Step 3: R + S = 5(a + b). This is divisible by 10 only if a + b is even. Take R = 5 and S = 10. Then R + S = 15, which is not divisible by 10. So (b) is not necessarily true.
Tip: for "not necessarily true", one counter-example is enough. Try the smallest numbers that fit the rules.
Answer as per the official UPSC answer key.
A person X was driving in a place where all roads ran either north-south or east-west, forming a grid. Roads are at a distance of 1 km from each other in a parallel. He started at the intersection of two roads, drove 3 km north, 3 km west and 4 km south. Which further route could bring him back to his starting point, if the same route is not repeated ?
Answer (b) & explanation
He should go 3 km east, then 1 km north (b). Step 1: he goes 3 km north and then 4 km south. So he ends 1 km south of the start. He also went 3 km west. Step 2: to get back, he must go 3 km east and 1 km north. Step 3: check the "no repeat" rule. Going east along the road 1 km south of the start is a new road, then 1 km north brings him home. Option (a) takes him further south. Option (c) takes him further west. Option (d) leaves him 3 km south of where he started.
Tip: in direction problems, add up north–south and east–west moves separately. The net gap in each direction tells you the way home.
Answer as per the official UPSC answer key.
Read the passage
By killing transparency and competition, crony capitalism is harmful to free enterprise, opportunity and economic growth. Crony capitalism, where rich and the influential are alleged to have received land and natural resources and various licences in return for payoffs to venal politicians, is now a major issue to be tackled. One of the greatest dangers to growth of developing economies like India is the middle-income trap where crony capitalism creates oligarchies that slow down the growth.
Which among the following is the most logical corollary to the above passage ?
Answer (c) & explanation
The logical corollary is the need for transparency and financial inclusion (c). Step 1: the passage says crony capitalism kills transparency and competition and keeps the poor away from licences and credit. Step 2: so the natural follow-up is more transparency and wider access to finance, which is option (c). Step 3: option (a), more welfare schemes, is never discussed. Option (b) mentions licences for the poor but not the transparency problem. Option (d), manufacturing over services, is not discussed at all.
Tip: a corollary is the solution that follows directly from the problem the passage names. Match the cure to the disease, here secrecy and exclusion.
Answer as per the official UPSC answer key.
A cylindrical overhead tank of radius 2 m and height 7 m is to be filled from an underground tank of size 5·5 m × 4 m × 6 m. How much portion of the underground tank is still filled with water after filling the overhead tank completely?
Answer (a) & explanation
One-third of the underground tank is still full (a). Step 1: the overhead tank is a cylinder. Volume = πr²h = 22/7 × 2 × 2 × 7 = 88 m³. Step 2: the underground tank is a cuboid. Volume = 5.5 × 4 × 6 = 132 m³. Step 3: water left = 132 − 88 = 44 m³. As a fraction: 44 ÷ 132 = 1/3. Option (b), 1/2, and options (c) and (d) do not fit. Here π = 22/7 cancels neatly with the 7 m height.
Tip: when the height is 7 or a multiple of 7, use 22/7 for π. It makes the numbers come out whole.
88/132 = 2/3 is what was taken out. The question asks what is left.
Answer as per the official UPSC answer key.
There is an order of 19000 quantity of a particular product from a customer. The firm produces 1000 quantity of that product per day out of which 5% are unfit for sale. In how many days will the order be completed?
Answer (c) & explanation
The order takes 20 days (c). Step 1: the firm makes 1000 pieces a day, but 5% are unfit. Good pieces per day = 95% of 1000 = 950. Step 2: the customer needs 19,000 good pieces. Days = 19,000 ÷ 950 = 20. Step 3: option (b), 19 days, is the trap: it divides 19,000 by 1000 and forgets the faulty pieces. Option (a), 18, is even less. Option (d), 22, is too many.
Tip: always work with the useful output, after removing waste or defects. A quick check: 950 × 20 = 19,000, which matches the order exactly.
Answer as per the official UPSC answer key.
The total emoluments of two persons are the same, but one gets allowances to the extent of 65% of his basic pay and the other gets allowances to the extent of 80% of his basic pay. The ratio of the basic pay of the former to the basic pay of the latter is :
Answer (d) & explanation
The ratio of their basic pays is 12 : 11 (d). Step 1: the first person's total is basic + 65% of basic = 1.65 × basic. The second person's total is 1.80 × basic. Step 2: the totals are equal, so 1.65 × B1 = 1.80 × B2. Step 3: B1 : B2 = 1.80 : 1.65. Multiply by 100 to get 180 : 165, then divide by 15 to get 12 : 11. The person with the smaller allowance must have the bigger basic pay. Option (a) 16 : 13 and option (b) 5 : 4 are traps from the 80 and 65 figures. Option (c) does not fit.
Tip: if a × X = b × Y, then X : Y = b : a. The ratio flips.
80 : 65 = 16 : 13 forgets that the total is basic + allowance.
Answer as per the official UPSC answer key.
In a class, there are 18 very tall boys. If these constitute three-fourths of the boys and the total number of boys is two-thirds of the total number of students in the class, what is the number of girls in the class?
Answer (b) & explanation
There are 12 girls (b). Step 1: 18 tall boys are three-fourths of the boys. So boys = 18 ÷ 3/4 = 24. Step 2: boys are two-thirds of all students. So students = 24 ÷ 2/3 = 36. Step 3: girls = 36 − 24 = 12. Option (a), 6, is a quarter of the boys, the boys who are not tall. Option (c), 18, is the number of tall boys. Option (d), 21, does not fit.
Tip: "x is a fraction of y" means y = x ÷ fraction. Work backwards one step at a time from the number you know. Check: girls are 12 of 36, which is one-third, the remaining part.
Answer as per the official UPSC answer key.
How many numbers are there between 100 and 300 which either begin with or end with 2?
Answer (a) & explanation
There are 110 such numbers (a). Step 1: between 100 and 300, the numbers that begin with 2 are 200 to 299. That is 100 numbers. Step 2: numbers that end with 2 and begin with 1 are 102, 112, 122 and so on up to 192. That is 10 numbers. The ones ending in 2 that begin with 2, like 202, are already counted. Step 3: total = 100 + 10 = 110. Option (b), 111, counts something twice. Options (c) and (d) do not fit.
Tip: for "either… or" counts, add the two groups and subtract the overlap. Here we simply skipped the overlap. This rule is called inclusion–exclusion.
adding 100 + 20 counts 202, 212, … twice.
Answer as per the official UPSC answer key.
Consider the following statement :
"We shall go either for a picnic or for trekking".
Which of the following, if true, would falsify this claim ?
Answer (d) & explanation
Only "we go for neither" falsifies the claim (d). Step 1: "We shall go either for a picnic or for trekking" means at least one of the two will happen. Step 2: such a claim is broken only when neither happens. So option (d) falsifies it. Step 3: test the others. Option (a), picnic but no trekking, fits the claim. Option (c), trekking but no picnic, also fits. Option (b), about health authorities, has nothing to do with whether the claim is true.
Tip: "either A or B" is false only when both are missing. "If A then B" is false only when A happens and B does not. Learn these two rules; they settle many logic questions.
Answer as per the official UPSC answer key.
Read the passage
Climate adaptation may be rendered ineffective if policies are not designed in the context of other development concerns. For instance, a comprehensive strategy that seeks to improve food security in the context of climate change may include a set of coordinated measures related to agricultural extension, crop diversification, integrated water and pest management and agricultural information services. Some of these measures may have to do with climate changes and others with economic development.
What is the most logical and rational inference that can be made from the above passage ?
Answer (d) & explanation
Climate adaptation should be examined together with other development options (d). Step 1: the passage says adaptation fails "if policies are not designed in the context of other development concerns". That is option (d). Step 2: option (c) says every development activity is linked to adaptation. The word "every" goes too far. Step 3: option (b) compares how complex food security and adaptation are, which the passage never does. Option (a), that adaptation is hard in developing countries, is not the main point.
Tip: the safest inference restates the author's main condition. Reject options with extreme words like "every" or comparisons the author never makes.
Answer as per the official UPSC answer key.
In a class of 60 students, where the number of girls is twice that of boys, Kamal, a boy, ranked seventeenth from the top. If there are 9 girls ahead of Kamal, the number of boys in rank after him is :
Answer (b) & explanation
12 boys rank after Kamal (b). Step 1: girls are twice the boys, and there are 60 students. So boys = 60 ÷ 3 = 20, girls = 40. Step 2: Kamal is 17th, so 16 students are ahead of him. Nine of them are girls, so 16 − 9 = 7 are boys. Step 3: boys after Kamal = 20 − 7 − 1 (Kamal himself) = 12. Option (a), 13, forgets to remove Kamal. Option (c), 7, is the boys ahead of him. Option (d), 3, does not fit.
Tip: in rank questions, always remember to count or remove the person himself. That is the most common mistake.
Answer as per the official UPSC answer key.
Read the passage
Biomass as fuel for power, heat, and transport has the highest mitigation potential of all renewable sources. It comes from agriculture and forest residues as well as from energy crops. The biggest challenge in using biomass residues is a long-term reliable supply delivered to the power plant at reasonable costs; the key problems are logistical constraints and the costs of fuel collection. Energy crops, if not managed properly, compete with food production and may have undesirable impacts on food prices. Biomass production is also sensitive to the physical impacts of a changing climate.
Projections of the future role of biomass are probably overestimated, given the limits to the sustainable biomass supply, unless breakthrough technologies substantially increase productivity. Climate-energy models project that biomass use could increase nearly four-fold to around 150 — 200 exajoules, almost a quarter of world primary energy in 2050. However the maximum sustainable technical potential of biomass resources (both residues and energy crops) without disruption of food and forest resources ranges from 80 — 170 exajoules a year by 2050, and only part of this is realistically and economically feasible. In addition, some climate models rely on biomass-based carbon capture and storage, an unproven technology, to achieve negative emissions and to buy some time during the first half of the century.
Some liquid biofuels such as corn-based ethanol, mainly for transport, may aggravate rather than ameliorate carbon emissions on a life-cycle basis. Second generation biofuels, based on ligno-cellulosic feedstocks — such as straw, bagasse, grass and wood — hold the promise of sustainable production that is high-yielding and emit low levels of greenhouse gases, but these are still in the R & D stage.
What is/are the present constraint/constraints in using biomass as fuel for power generation ?
- 1. Lack of sustainable supply of biomass
- 2. Biomass production competes with food production
- 3. Bio-energy may not always be low carbon on a life-cycle basis
Select the correct answer using the code given below :
Answer (d) & explanation
All three constraints are right (d). Step 1: the passage mentions limits to "sustainable biomass supply". So statement 1, lack of a steady supply, is a constraint. Step 2: it says energy crops "compete with food production". So statement 2 is a constraint too. Step 3: it adds that biofuels "may aggravate" emissions "on a life-cycle basis". So bio-energy is not always low carbon, and statement 3 is right as well. Options (a), (b) and (c) each leave out at least one of the stated limits.
Tip: when every statement matches a line in the passage, pick "all of the above". Do not leave one out just because the full option seems too easy.
Answer as per the official UPSC answer key.
A person is standing on the first step from the bottom of a ladder. If he has to climb 4 more steps to reach exactly the middle step, how many steps does the ladder have?
Answer (b) & explanation
The ladder has 9 steps (b). Step 1: he is on step 1 and climbs 4 more steps, so the middle step is step 5. Step 2: a middle step has the same number of steps below and above it. There are 4 steps below step 5. So there must be 4 above. Step 3: total = 4 + 1 + 4 = 9 steps. Option (a), 8, has no single middle step. Option (c), 10, also has no single middle step. Option (d), 11, would put the middle at step 6.
Tip: a "middle" item exists only when the total is odd. For an odd total n, the middle item is number (n + 1) ÷ 2. Here (9 + 1) ÷ 2 = 5, which checks out.
Answer as per the official UPSC answer key.
Consider the following statements :
- 1. Either A and B are of the same age or A is older than B
- 2. Either C and D are of the same age or D is older than C
- 3. B is older than C
Which of the following conclusions can be drawn from the above statements ?
Answer (d) & explanation
A is older than C (d). Step 1: write each statement as a sign. Statement 1: A is the same age as or older than B, so A ≥ B. Statement 2: D ≥ C. Statement 3: B > C. Step 2: join them: A ≥ B and B > C, so A > C for certain. Step 3: test the others. Option (a), A older than B, is only possible, since A and B may be equal. Option (c), D older than C, is also only possible, since they may be equal. Option (b), B and D the same age, is never linked by any statement.
Tip: turn age words into ≥ and > signs. A chain with a strict ">" anywhere gives a strict ">" at the end.
Answer as per the official UPSC answer key.
Read the passage
As we look to 2050, when we will need to feed two billion more people, the question of which diet is best has taken on new urgency. The foods we choose to eat in the coming decades will have dramatic ramifications for the planet. Simply put, a diet that revolves around meat and dairy, a way of eating that is on the rise throughout the developing world, will take a greater toll on the world’s resources than one that revolves around unrefined grains, nuts, fruits and vegetables.
What is the critical message conveyed by the above passage ?
Answer (a) & explanation
The critical message is that more animal-based food puts a bigger burden on natural resources (a). Step 1: the passage says a diet rich in meat and dairy "will take a greater toll on the world's resources". That is option (a). Step 2: option (b) says plant diets are best for health in developing countries. But the passage judges diets by their effect on the planet, not on health. Step 3: option (c), about people changing habits regardless of health, is not the point. Option (d), that we do not know the best diet, misses the main concern.
Tip: animal food needs much more land, water and feed per calorie than plant food. This is a common theme in climate passages.
Answer as per the official UPSC answer key.