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.
X said to Y, "At the time of your birth I was twice as old as you are at present." If the present age of X is 42 years, then consider the following statements :
- 1. 8 years ago, the age of X was five times the age of Y.
- 2. After 14 years, the age of X would be two times the age of Y.
Which of the above statements is/are correct ?
Answer (b) & explanation
Only statement 2 is correct (b). Step 1: when Y was born, X's age equalled the age gap. That gap is twice Y's present age. So X − Y = 2Y, which means X = 3Y. With X = 42, Y = 14. Step 2: statement 1: 8 years ago, X was 34 and Y was 6. 34 is not 5 × 6 = 30, so it is false. Step 3: statement 2: after 14 years, X will be 56 and Y 28. 56 = 2 × 28, so it is true. Options (a), (c) and (d) fail.
Tip: the age gap between two people never changes. "At your birth I was ..." gives you that gap directly.
Answer as per the official UPSC answer key.
Read the passage
A central message of modern development economics is the importance of income growth, by which is meant growth in Gross Domestic Product (GDP). In theory, rising GDP creates employment and investment opportunities. As incomes grow in a country where the level of GDP was once low, households, communities, and governments are increasingly able to set aside some funds for the production of things that make for a good life. Today GDP has assumed such a significant place in the development lexicon, that if someone mentions “economic growth”, we know they mean growth in GDP.
With reference to the above passage, the following assumptions have been made :
- 1. Rising GDP is essential for a country to be a developed country.
- 2. Rising GDP guarantees a reasonable distribution of income to all households.
Which of the above assumptions is/are valid ?
Answer (d) & explanation
Neither assumption is valid (d). Step 1: the passage reports what development economics says "in theory" about GDP. It does not call GDP growth essential for becoming developed. So assumption 1 fails. Step 2: assumption 2 says rising GDP guarantees fair income for all households. The passage says nothing about distribution. So 2 fails. Step 3: options (a), (b) and (c) fail.
Tip: reporting a theory is not endorsing it. Also, "guarantees" is a very strong word. GDP measures total output; it can rise even while inequality grows, which is why measures like the Human Development Index exist.
Answer as per the official UPSC answer key.
In a code language 'MATHEMATICS' is written as 'LBSIDNZUHDR'. How is 'CHEMISTRY' written in that code language ?
Answer (b) & explanation
CHEMISTRY is written BIDNHTSSX (b). Step 1: compare MATHEMATICS with LBSIDNZUHDR letter by letter. M → L (−1), A → B (+1), T → S (−1), H → I (+1). The moves alternate −1, +1. Step 2: apply this to CHEMISTRY: C−1 = B, H+1 = I, E−1 = D, M+1 = N, I−1 = H, S+1 = T, T−1 = S, R+1 = S, Y−1 = X. Step 3: the code is BIDNHTSSX. Option (c) has L and T, getting M wrong. Options (a) and (d) start with the wrong move.
Tip: in coding questions, check the first four letters to find the pattern. Then look at only the letters where the options differ.
Answer as per the official UPSC answer key.
Read the passage
A study conducted on the impacts of climate change over the Cauvery basin of Tamil Nadu using regional climate models showed an increasing trend for maximum and minimum temperatures, and a decrease in the number of rainy days. These climatic shifts will have an impact on the hydrological cycles in the region, lead to more run-off and less recharge, and affect the groundwater tables. Further, there has been an increase in the frequency of droughts in the State. This has driven farmers to increase dependency on groundwater resources to secure their crops.
Which one of the following statements best reflects the crux of the passage given above ?
Answer (c) & explanation
The crux is that climate change makes water more critical while also threatening it (c). Step 1: the passage says climate change cuts groundwater recharge. At the same time, more droughts raise farmers' dependence on groundwater. So water becomes more important and more at risk together. That is (c). Step 2: options (a) and (b) bring in remedies: regional climate models and dry-land cropping. The passage's main point is the problem, not these fixes. Step 3: option (d), farmers adopting risky livelihoods, is a side detail, not the crux.
Tip: the crux captures the passage's central tension. When a passage shows a "double squeeze", choose the option that names both sides.
Answer as per the official UPSC answer key.
In a group of 120 persons, 80 are Indians and rest are foreigners. Further, 70 persons in the group can speak English. The number of Indians who can speak English is
Answer (d) & explanation
The number of Indians who speak English is 30 or more (d). Step 1: there are 120 people: 80 Indians and 40 foreigners. Step 2: 70 people speak English. Even if all 40 foreigners speak English, at least 70 − 40 = 30 speakers must be Indian. Step 3: if fewer foreigners speak English, more Indians must. It can go up to all 70. So the answer is "30 or more". Option (a), exactly 20, is impossible, and option (b), exactly 30, is only the least case. Option (c), 30 or less, gets the direction wrong.
Tip: for "at least" questions, give the other group the most it can take. What is left is the minimum for your group.
the question asks for what must be true. Find the smallest overlap, not an exact number.
Answer as per the official UPSC answer key.
Consider the following statements :
- 1. The sum of 5 consecutive integers can be 100.
- 2. The product of three consecutive natural numbers can be equal to their sum.
Which of the above statements is/are correct ?
Answer (c) & explanation
Both statements are correct (c). Step 1: the sum of 5 consecutive integers is 5 × the middle one. 100 = 5 × 20, so 18 + 19 + 20 + 21 + 22 = 100. Statement 1 is true. Step 2: for statement 2, try small natural numbers: 1 × 2 × 3 = 6, and 1 + 2 + 3 = 6. They are equal, so statement 2 is true. Step 3: so options (a), (b) and (d) fail.
Tip: for consecutive numbers, the sum = count × middle value (with an odd count). For "can be" statements, one example is enough to prove it true.
Answer as per the official UPSC answer key.
Read the passage
A social and physical environment riddled with poverty, inequities, unhygienic and insanitary conditions generates the risk of infectious diseases. Hygiene has different levels : personal, domestic and community hygiene. There is no doubt that personal cleanliness brings down the rate of infectious diseases. But the entry of the market into this domain has created a false sense of security that gets conditioned and reinforced by the onslaught of advertisements. Experience in Western Europe shows that along with personal hygiene, general improvements in environmental conditions and components like clean water, sanitation and food security have brought down infant/child death/infection rates considerably. The obsession with hand hygiene also brings in the persisting influence of the market on personal health, overriding or marginalising the negative impact on ecology and the emergence of resistant germs.
On the basis of the passage given above, the following assumptions have been made :
- 1. People who are obsessed with personal hygiene tend to ignore the community hygiene.
- 2. Emergence of multi-drug resistant germs can be prevented by personal cleanliness.
- 3. Entry of the market in the domain of hygiene increases the risk of infectious diseases.
- 4. Scientific and micro-level interventions are not sufficient to bring down the burden of infectious diseases.
- 5. It is community hygiene implemented through public health measures that is really effective in the battle against infectious diseases.
Which of the above assumptions are valid ?
Answer (c) & explanation
Assumptions 4 and 5 are valid (c). Step 1: the passage says Western Europe cut infections through clean water, sanitation, food security and hygiene for all. So small-scale, personal steps are not enough (4), and community hygiene through public health works (5). Step 2: assumption 3 says the market raises the risk. The passage says the market creates a false sense of security, not higher risk. Step 3: assumption 2 says personal cleanliness can prevent drug-resistant germs; not supported. Assumption 1 is also not stated. So options (a), (b) and (d) fail.
Tip: "false sense of security" is not the same as "increased risk". Check the exact claim, not just the topic.
Answer as per the official UPSC answer key.
Half of the villagers of a certain village have their own houses. One-fifth of the villagers cultivate paddy. One-third of the villagers are literate. Four-fifth of the villagers are under 25 years of age. Which one of the following statements is certainly correct ?
Answer (b) & explanation
The statement certainly correct is that some villagers under 25 are literate (b). Step 1: four-fifths are under 25 and one-third are literate. Add them: 4/5 + 1/3 = 17/15, which is more than the whole village. Step 2: two groups that together exceed the total must overlap. So some literate villagers must be under 25. That is (b). Step 3: options (a), (c) and (d) link houses, paddy and age in exact ways. The data give no such link, so none is certain.
Tip: if two fractions of the same group add up to more than 1, the groups must share members. The overlap is at least the excess (here 2/15).
Answer as per the official UPSC answer key.
If the price of an article is decreased by 20% and then the new price is increased by 25%, then what is the net change in the price ?
Answer (a) & explanation
There is no net change, 0% (a). Step 1: a 20% cut means multiplying by 0.8. Step 2: a 25% rise on the new price means multiplying by 1.25. Step 3: 0.8 × 1.25 = 1. So the final price equals the starting price. Options (b) and (c) wrongly add or subtract the percentages (25 − 20 = 5). Option (d) is wrong because the multipliers settle it without knowing the price.
Tip: for successive percentage changes, multiply the factors. A shortcut is a + b + ab/100: −20 + 25 − 500/100 = 0.
don't just add –20 and +25. The 25% is taken on the reduced price.
Answer as per the official UPSC answer key.
Seven books P, Q, R, S, T, U and V are placed side by side. R, Q and T have blue covers and other books have red covers. Only S and U are new books and the rest are old. P, R and S are law reports; the rest are Gazetteers. Books of old Gazetteers with blue covers are
Answer (c) & explanation
The old Gazetteers with blue covers are Q and T (c). Step 1: list each group. Gazetteers: all except the law reports P, R and S, so Q, T, U, V. Step 2: old books: all except the new ones S and U, so P, Q, R, T, V. Blue covers: Q, R, T. Step 3: books in all three groups: Q and T. Option (a) includes R, a law report. Options (b) and (d) include U, a new book.
Tip: in grouping puzzles, write each list and find the common members. Using "all except" lists helps avoid errors when a group is described by what it is not.
Answer as per the official UPSC answer key.
At which one of the following times, do the hour hand and the minute hand of the clock make an angle of 180° with each other ?
Answer (d) & explanation
The hands are opposite between 7:05 and 7:10 (d). Step 1: the angle between the hands is |30H − 5.5M|, where H is the hour and M the minutes. At 7:00 it is 30 × 7 = 210°, so (a) fails. Step 2: as minutes pass, the minute hand closes the gap at 5.5° per minute. We need 210 − 5.5M = 180, so M = 30 ÷ 5.5 ≈ 5.45 minutes. Step 3: so the hands are 180° apart at about 7:05:27. That is just after 7:05, so (b) and (c) fail.
Tip: the minute hand gains 5.5° per minute on the hour hand. This one fact solves most clock-angle questions.
at 7:00 the angle is 210°, not 180°. The minute hand has to catch up 30°.
Answer as per the official UPSC answer key.
Read the passage
Researchers were able to use stem cells to gauge the neurotoxic effects of the environmental pollutant Bisphenol A (BPA). They used a combination of biochemical and cell-based assays to examine the gene expression profile during the differentiation of mouse embryonic stem cells upon treatment with BPA, a compound known to cause heart diseases, diabetes, and developmental abnormalities in humans. They were able to detect and measure BPA toxicity towards the proper specification of primary germ layers, such as endoderm and ectoderm, and the establishment of neural progenitor cells.
On the basis of the passage given above, the following assumptions have been made :
- 1. BPA may alter embryonic development in vivo.
- 2. Biochemical and cell-based assays are useful in finding out treatments for pollution-induced diseases.
- 3. Embryonic stem cells could serve as a model to evaluate the physiological effects of environmental pollutants.
Which of the above assumptions are valid ?
Answer (c) & explanation
Assumptions 1 and 3 are valid (c). Step 1: the passage says BPA (a chemical in some plastics) harmed the formation of germ layers in stem cells. Germ layers are the first steps of an embryo's growth. So BPA may alter embryo development in the body (1). Step 2: the study used embryonic stem cells as a test model. So they can serve as a model to study pollutants (3). Step 3: assumption 2 says the assays help find treatments. But the assays measured toxicity; treatments are not discussed. So options (a), (b) and (d) fail.
Tip: "in vivo" means in a living body; "in vitro" means in a lab dish. Separate what a study measured from what it might later lead to.
Answer as per the official UPSC answer key.
Consider all 3-digit numbers (without repetition of digits) obtained using three non-zero digits which are multiples of 3. Let S be their sum. Which of the following is/are correct ?
- 1. S is always divisible by 74.
- 2. S is always divisible by 9.
Select the correct answer using the code given below :
Answer (c) & explanation
Both statements are correct (c). Step 1: the non-zero digits that are multiples of 3 are 3, 6 and 9. Without repeating digits, they make 3 × 2 × 1 = 6 numbers. Step 2: each digit appears in each place (hundreds, tens, units) twice. So S = 2 × (3 + 6 + 9) × 111 = 36 × 111 = 3996. Step 3: 3996 = 74 × 54, so it is divisible by 74 (statement 1). Its digits add up to 27, so it is divisible by 9 (statement 2). So options (a), (b) and (d) fail.
Tip: for the sum of all numbers made from given digits, use (number of times each digit sits in a place) × (sum of digits) × 111.
Answer as per the official UPSC answer key.
A cubical vessel of side 1 m is filled completely with water. How many millilitres of water is contained in it (neglect thickness of the vessel) ?
Answer (d) & explanation
The vessel holds 10,00,000 ml (d). Step 1: the vessel is a cube of side 1 m, so its volume is 1 m³. Step 2: 1 m³ = 1000 litres. Step 3: 1 litre = 1000 ml. So 1000 × 1000 = 10,00,000 ml (one million). Option (a), 1000, is the number of litres, not millilitres. Options (b) and (c) drop zeroes.
Tip: remember 1 m³ = 1000 litres and 1 cm³ = 1 ml. So 1 m³ = 100 × 100 × 100 cm³ = 10,00,000 ml.
1000 is the answer in litres. The question asks for millilitres.
Answer as per the official UPSC answer key.
A Statement followed by Conclusion-I and Conclusion-II is given below. You have to take the Statement to be true even if it seems to be at variance from the commonly known facts. Read all Conclusions and then decide which of the given Conclusion(s) logically follows/follow from the Statement, disregarding the commonly known facts.
Statement : Some cats are almirahs. Some almirahs are chairs. All chairs are tables.
Conclusion-I : Certainly some almirahs are tables.
Conclusion-II : Some cats may not be chairs.
Which one of the following is correct ?
Answer (c) & explanation
Both conclusions follow (c). Step 1: some almirahs are chairs, and all chairs are tables. So those almirahs are also tables. Conclusion I, "certainly some almirahs are tables", is true. Step 2: nothing links cats to chairs directly. So it is possible that some cats are not chairs. Conclusion II uses "may not", which only claims a possibility. Step 3: so both follow. Options (a), (b) and (d) fail.
Tip: "may" or "may not" conclusions follow whenever the case is possible and not ruled out. "Certainly" conclusions need a firm chain, like "some A are B, all B are C".
a 'may' conclusion follows whenever the statements leave that case open.
Answer as per the official UPSC answer key.
Consider two Statements and a Question :
Statement-1 : The last day of the month is a Wednesday.
Statement-2 : The third Saturday of the month was the seventeenth day.
Question : What day is the fourteenth of the given month ?
Which one of the following is correct in respect of the Statements and the Question ?
Answer (b) & explanation
Statement-2 alone is sufficient (b). Step 1: Statement-2 says the third Saturday was the 17th. The 14th is 3 days earlier. Three days before Saturday is Wednesday. So Statement-2 alone answers it. Step 2: Statement-1 says the last day is a Wednesday. But we do not know whether the month has 28, 29, 30 or 31 days. So the 14th could fall on different days. Step 3: so (a) fails, and since Statement-2 works alone, (c) and (d) fail too.
Tip: a fixed date with a known weekday is the best anchor. A clue about "the last day" fails when the month's length is unknown.
Answer as per the official UPSC answer key.
When a certain number is multiplied by 7, the product entirely comprises ones only (1111...). What is the smallest such number ?
Answer (d) & explanation
The smallest number is 15873 (d). Step 1: multiply each option by 7 and look for an answer made only of ones. Step 2: 15873 × 7 = 111111. That works. Step 3: the others fail: 15713 × 7 = 109991, 15723 × 7 = 110061 and 15783 × 7 = 110481. Also, 111111 is the smallest all-ones number divisible by 7 (1, 11, 111, 1111 and 11111 are not). So (d).
Tip: 111111 = 3 × 7 × 11 × 13 × 37. It is a handy number: divisible by 7, 11 and 13 together.
Answer as per the official UPSC answer key.
Replace the incorrect term by the correct term in the given sequence
3, 2, 7, 4, 13, 10, 21, 18, 31, 28, 43, 40
where odd terms and even terms follow the same pattern.
Answer (a) & explanation
The incorrect term 2 should be replaced by 0 (a). Step 1: odd places: 3, 7, 13, 21, 31, 43. The gaps are 4, 6, 8, 10, 12. Step 2: even places: 2, 4, 10, 18, 28, 40. The gaps from 4 on are 6, 8, 10, 12, matching the odd places. So the first gap must also be 4. Step 3: the first even term should be 4 − 4 = 0, not 2. Options (b), (c) and (d) give a wrong first gap.
Tip: when a question says two sub-series follow the same pattern, find the pattern in the clean one, then fix the other. Each even term here is 3 less than its odd partner.
Answer as per the official UPSC answer key.
In an objective type test of 90 questions, 5 marks are allotted for every correct answer and 2 marks are deducted for every wrong answer. After attempting all the 90 questions, a student got a total of 387 marks. What is the number of incorrect responses ?
Answer (a) & explanation
The student gave 9 wrong answers (a). Step 1: if all 90 were right, the score would be 90 × 5 = 450. Step 2: each wrong answer loses the 5 marks it would have earned and costs 2 more. So each wrong answer reduces the score by 7. Step 3: the score fell by 450 − 387 = 63. So wrong answers = 63 ÷ 7 = 9. Check: 81 × 5 − 9 × 2 = 405 − 18 = 387. Options (b), (c) and (d) fail this check.
Tip: in negative-marking questions, assume all are correct, then divide the shortfall by (marks for right + penalty for wrong).
Answer as per the official UPSC answer key.
If 32019 is divided by 10, then what is the remainder ?
Answer (c) & explanation
The remainder is 7 (c). Step 1: the remainder on dividing by 10 is just the unit digit. Step 2: powers of 3 end in a repeating cycle: 3¹ = 3, 3² = 9, 3³ = 27, 3⁴ = 81. The cycle is 3, 9, 7, 1, of length 4. Step 3: 2019 ÷ 4 leaves a remainder of 3 (2019 = 4 × 504 + 3). So take the 3rd term of the cycle: 7. Option (b), 3, is the first term. Options (a) and (d) are the 4th and 2nd terms.
Tip: unit digits of powers repeat every 4 (or fewer). Divide the power by 4 and use the remainder; a remainder of 0 means the 4th term.
Answer as per the official UPSC answer key.