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.
A person facing the East travels 4 km straight and then turns right and travels 3 km, then further turns left and travels 2 km and finally turns left and travels 3 km. The minimum distance between the final point and the initial point, and the direction in which the person is facing at the final point are, respectively
Answer (d) & explanation
He ends 6 km away, facing North (d). Step 1: trace the path. Facing East, he walks 4 km East. A right turn faces South: 3 km. A left turn faces East: 2 km. A left turn faces North: 3 km. Step 2: South 3 and North 3 cancel out. East total = 4 + 2 = 6 km. So he is 6 km east of the start. Step 3: his last walk was northward, so he is facing North. Option (b) has the right distance but the wrong direction. Options (a) and (c) add the distances wrongly.
Tip: track north-south and east-west separately; opposite moves cancel. The final facing direction is simply the direction of the last walk.
Answer as per the official UPSC answer key.
Question : If x and y are integers, then is x even?
Statement I : x2y2 is even.
Statement II : 1 + x2 + y2 is odd.
Answer (c) & explanation
Both statements together are needed (c). Step 1: Statement I: x²y² is even, so xy is even. That means at least one of x and y is even. x might be odd if y is even. Not enough. Step 2: Statement II: 1 + x² + y² is odd, so x² + y² is even. That means x and y have the same parity (both odd or both even). Not enough. Step 3: together: same parity, and at least one even, so both are even. Hence x is even. Options (a), (b) and (d) fail.
Tip: remember odd + odd = even, even + even = even, odd + even = odd. A square keeps the parity of its number.
Answer as per the official UPSC answer key.
Seven persons A, B, C, D, E, F and G travel by three cars X, Y, Z. A and another two of them travel by X. Only E travels with G. C travels by Z, but B does not travel by Y. Besides, A and B do not travel by the same car. Then which of the following are correct?
- I. No one travels alone.
- II. Only D travels with F.
- III. Only C travels with B.
Select the answer using the code given below.
Answer (b) & explanation
1. B is not in Y and not with A (in X), so B is in Z with C.
2. E and G form a car of their own; X already has A and Z has B and C, so E and G are in Y. D and F join A in X.
3. Cars: X = A, D, F; Y = E, G; Z = B, C. I and III are true. II is false, because A also travels with F.
Answer as per the official UPSC answer key.
If ZERO is encoded as ADSN, then how do you encode STOP?
Answer (b) & explanation
STOP is encoded as TSPO (b). Step 1: compare ZERO and ADSN letter by letter: Z → A (+1, wrapping round), E → D (−1), R → S (+1), O → N (−1). The moves alternate +1, −1. Step 2: apply to STOP: S + 1 = T, T − 1 = S, O + 1 = P, P − 1 = O. Step 3: so STOP becomes TSPO. Options (a) SPOT, (c) TSOP and (d) POST are rearrangements that do not follow the rule.
Tip: in letter codes, write the shift for each position. Remember that after Z comes A again. Options that are real words are often traps.
Answer as per the official UPSC answer key.
Eight persons P, Q, R, S, T, U, V and W sit around a round table in eight different seats placed with equal distance between any two consecutive seats. Both P and R are adjacent to Q. Both T and R are adjacent to S. Both U and W are adjacent to V. S and W are on opposite chairs. If while going in the clockwise direction around the table from P, one meets R before T, then how many persons shall Q cross while moving in the clockwise direction around the table before meeting W?
Answer (a) & explanation
1. P–Q–R and R–S–T join into one run P, Q, R, S, T. Clockwise from P, R comes before T, so number the seats 1 to 8 clockwise: P 1, Q 2, R 3, S 4, T 5.
2. U, V, W take seats 6, 7, 8 with V in the middle (seat 7). W must face S (seat 4), so W is at seat 8 and U at 6.
3. Clockwise from Q: R, S, T, U, V, then W. Q crosses 5 persons.
Answer as per the official UPSC answer key.
Read the passage
The key source of the battle for clean skies and clear lungs is the fuel we burn—from household Chulhas to the thermal power plants. In most cases, it is biomass or coal. The Supreme Court banned the use of pet coke—the dirtiest of such fuels. The Delhi Government banned the use of coal, which was later extended to the entire National Capital Region. It was also agreed that the thermal power plants would clean up or shut down. Action on this has been patchy to say the least. The lesson from the transition to CNG is that people need alternatives for a ban to be effective. When diesel buses were stopped, CNG supply had to be assured. It also had to be feasible in terms of cost. The Supreme Court agreed that fiscal measures were needed to keep clean fuel cheaper than dirty fuel. Now even as coal is banned, the price of natural gas makes industry uncompetitive.
Which of the following inferences is/are correct?
- 1. The source of the energy we consume is the key to the battle for cleaner air.
- 2. Bans are effective where the will is strong and the people are convinced that such bans are for the greater good of society.
- 3. There is judicial approval for a policy that intervenes fiscally to facilitate benevolent pricing for cleaner fuel.
Select the answer using the code given below.
Answer (c) & explanation
Inferences 1 and 3 are correct (c). Step 1: the passage opens: the key to clean skies is "the fuel we burn". So the source of energy is central (1). Step 2: it says "the Supreme Court agreed that fiscal measures were needed to keep clean fuel cheaper than dirty fuel". That is judicial approval for pricing help (3). Step 3: inference 2 says bans work when people are convinced they are for the greater good. But the passage says bans work when people have alternatives at a feasible cost, like CNG. So options (a), (b) and (d) fail.
Tip: find the passage's own reason; do not accept a different reason that sounds good. Delhi's switch of buses to CNG followed Supreme Court orders around 2001–02.
Answer as per the official UPSC answer key.
Three partners A, B and C entered into a business. A invested one-third of the capital for one-third duration. B invested one-fourth of the capital for one-fourth duration. C invested the remaining capital for the whole duration. Out of a profit of ₹ 17,000, how much profit will C get?
Answer (a) & explanation
C gets ₹12,000 (a). Step 1: profit is shared in the ratio of capital × time. A: 1/3 of capital for 1/3 of the time = 1/9. B: 1/4 for 1/4 = 1/16. C put in the rest: 1 − 1/3 − 1/4 = 5/12, for the whole time = 5/12. Step 2: multiply by 144 to clear fractions: A : B : C = 16 : 9 : 60. Total = 85 parts. Step 3: C's share = 60/85 × 17,000 = ₹12,000. Options (b), (c) and (d) fail.
Tip: in partnerships, multiply capital by time for each partner. Clear fractions with the LCM of the denominators before sharing.
Answer as per the official UPSC answer key.
The class average x in a test increases by 4 when the score of a student is rectified, whose corrected score is 100 instead of 0. Later, the score of another student was found to have been recorded as 81 in place of 56. If there are no other corrections and the final corrected average is y, then y − x is
Answer (b) & explanation
y − x is 3 (b). Step 1: one student's score rose by 100 (from 0 to 100), and the average rose by 4. So the class has 100 ÷ 4 = 25 students. Step 2: the second correction changes 81 to 56: the total falls by 25 marks. Shared by 25 students, the average falls by 1. Step 3: overall, the average went up by 4 and then down by 1: y − x = 3. Options (a), (c) and (d) fail.
Tip: change in average = change in total ÷ number of people. Use the first correction to find the class size, then reuse it.
x is the average before both corrections, so both changes count.
Answer as per the official UPSC answer key.
In a sequence of numbers, each number other than the first two is the sum of the two immediately preceding numbers from it. If the first two numbers in the sequence are 4 and 7, then the sixth number is
Answer (d) & explanation
The sixth number is 47 (d). Step 1: the rule: each number after the first two is the sum of the two before it. Step 2: start with 4 and 7. Third: 4 + 7 = 11. Fourth: 7 + 11 = 18. Fifth: 11 + 18 = 29. Step 3: sixth: 18 + 29 = 47. Option (a), 29, is the fifth number, a common slip from miscounting positions. Options (b) and (c) are wrong sums.
Tip: this is a Fibonacci-style sequence. Write out every term and number its position so you do not stop one step early. The classic Fibonacci series starts 1, 1, 2, 3, 5, 8.
Answer as per the official UPSC answer key.
Question : X is a collection of certain odd numbers whereas Y is a collection of certain even numbers. T consists of the numbers all of which are either from X or from Y. Is every number of T from Y?
Statement I : The sum of any two numbers belonging to T is even.
Statement II : If both p and q are picked from T, then (p – 1)q is even.
Answer (d) & explanation
Even both statements together are not enough (d). Step 1: Statement I: any two numbers in T add to an even number. That happens only if T is all odd or all even. Step 2: Statement II: (p − 1)q is even for any p, q in T. If T is all odd, p − 1 is even, so it holds. If T is all even, q is even, so it holds. Both cases still allowed. Step 3: an all-odd T (from X) fits both statements, and so does an all-even T (from Y). So we cannot say every number is from Y. Options (a), (b) and (c) fail.
Tip: test each statement on both possible cases. If a case survives every statement, the data is not enough.
Answer as per the official UPSC answer key.
There are four statements X, Y, Z and W. Their relations are as follows :
If X is incorrect, then so is Z; if Y is incorrect, then W is correct; if W is correct, then X is incorrect.
Which of the following is/are correct?
- I. If X is correct, then so is Y.
- II. If Z is correct, then it is not necessary that Y is correct.
Select the answer using the code given below.
Answer (a) & explanation
Only statement I is correct (a). Step 1: turn each rule around (the contrapositive, which is always equally true): "X incorrect → Z incorrect" becomes Z correct → X correct. "Y incorrect → W correct" becomes W incorrect → Y correct. "W correct → X incorrect" becomes X correct → W incorrect. Step 2: statement I: X correct → W incorrect → Y correct. So I is true. Step 3: statement II: Z correct → X correct → W incorrect → Y correct. So Y must be correct; II says it is not necessary, which is false. Options (b), (c) and (d) fail.
Tip: "If A then B" also means "if not B then not A". Chaining contrapositives solves most such puzzles.
only the contrapositive of an 'if … then' is safe. Here it links all four statements into one chain.
Answer as per the official UPSC answer key.
There are three types of rectangular tiles : 3' × 3', 3' × 7' and 3' × 11'. An area of rectangular shape of dimensions 3' × 100' is to be covered using these tiles without breaking them. If x and y are the maximum and minimum numbers of tiles of various sizes, respectively, that can be used to cover the area exactly, then x – y is
Answer (a) & explanation
x − y is 20 (a). Step 1: every tile is 3' wide, like the strip, so only lengths matter: 3a + 7b + 11c = 100, where a, b, c are the numbers of each tile. Step 2: maximum tiles: use as many short 3' tiles as possible. 100 is not a multiple of 3, but 31 × 3 + 7 = 100. So x = 32 tiles. Step 3: minimum tiles: use as many long 11' tiles as possible. 9 × 11 = 99 leaves 1 (impossible); trying downwards, 8 × 11 + 4 × 3 = 88 + 12 = 100 works with 12 tiles, and no combination with 11 or fewer tiles works. So y = 12. x − y = 20.
Tip: for maximum count, use the smallest pieces; for minimum, the largest. Then adjust to hit the exact total.
Answer as per the official UPSC answer key.
The top of a table is rectangular and its dimensions are 6′ × 10′. Two rectangular portions of the table top are painted in blue colour; both these portions have dimensions 2.5′ × 8′ and each of them has exactly two sides common with two edges of the table top. If the table is fixed to the ground and the remaining portion of the table top is painted in white, how many different patterns are possible when observed from above?
Answer (b) & explanation
Four patterns are possible (b). Step 1: each blue strip is 2.5′ × 8′. Its 8′ side cannot lie along the 6′ edge, so it lies along a 10′ edge, and it touches two edges, so it sits in a corner. Step 2: two strips on the same 10′ edge would need 8 + 8 = 16′, more than 10′, so they would overlap and merge into one shape. So one strip goes along each 10′ edge. Step 3: each strip can sit at the left or right end of its edge: 2 × 2 = 4 patterns. The table is fixed, so mirror images count as different. Options (a), (c) and (d) miscount.
Tip: in arrangement puzzles, first use the sizes to rule out positions. Then count the free choices and multiply.
Answer as per the official UPSC answer key.
Read the passage
The key source of the battle for clean skies and clear lungs is the fuel we burn—from household Chulhas to the thermal power plants. In most cases, it is biomass or coal. The Supreme Court banned the use of pet coke—the dirtiest of such fuels. The Delhi Government banned the use of coal, which was later extended to the entire National Capital Region. It was also agreed that the thermal power plants would clean up or shut down. Action on this has been patchy to say the least. The lesson from the transition to CNG is that people need alternatives for a ban to be effective. When diesel buses were stopped, CNG supply had to be assured. It also had to be feasible in terms of cost. The Supreme Court agreed that fiscal measures were needed to keep clean fuel cheaper than dirty fuel. Now even as coal is banned, the price of natural gas makes industry uncompetitive.
Which of the following statements is/are correct?
- 1. Thermal power stations in Delhi were required to summarily shut down.
- 2. CNG supplies had to be assured once diesel vehicles were prohibited from plying.
- 3. The Supreme Court banned the use of coal across the National Capital Region.
Select the answer using the code given below.
Answer (c) & explanation
Only statement 2 is correct (c). Step 1: statement 2 matches: "When diesel buses were stopped, CNG supply had to be assured." Correct. Step 2: statement 1 says thermal plants had to summarily shut down. The passage says they would "clean up or shut down", a choice, not an immediate closure. Wrong. Step 3: statement 3 says the Supreme Court banned coal across NCR. The passage says the Delhi Government banned coal, later extended to NCR; the Court banned pet coke. Wrong. Options (a), (b) and (d) fail.
Tip: check who did what. Swapping the actor (Court versus Government) is a common trap in fact-based passages.
Answer as per the official UPSC answer key.
There are two chemicals which do not react with each other. A container contains 10 litres of the chemical A. One litre of this chemical is removed from it and one litre of the chemical B is poured. Then one litre of the mixture is removed from the container and one litre of B is poured. If this process of replacing one litre of the mixture by one litre of B is performed once more, then what is the volume of B that is present in the container approximately (in percentage)?
Answer (b) & explanation
B is about 27% of the container (b). Step 1: each time, 1 litre of the 10-litre mixture is removed, so 9/10 of chemical A stays. Step 2: after three rounds, A left = 10 × (9/10)³ = 10 × 0.729 = 7.29 litres, that is 72.9%. Step 3: the rest is B: 100 − 72.9 = 27.1%, about 27%. Option (a), 25, and the others come from subtracting 10% three times or similar slips.
Tip: for repeated replacement, use: original left = start × (1 − removed/total)ⁿ. Simple subtraction of 10% each time gives the wrong answer.
it is not 3 × 10% = 30%. Later rounds take out some B as well.
Answer as per the official UPSC answer key.
Read the passage
When SARS-CoV-2 was first detected in 2019, it was a truly novel virus for the world. At that time, no one in the world had been exposed to SARS-CoV-2 or had specific immunity against it. In contrast, people across the world have been exposed to HMPV for decades and the virus is well-studied. HMPV and SARS-CoV-2 belong to two very different virus families with fundamentally different characteristics and epidemiology, with strong seasonality seen in HMPV, unlike SARS-CoV-2. Both viruses cause different severity of symptoms, particularly over the long term, and the affected population segments do not fully overlap. In general, HMPV causes milder illness with deaths being very rare and with no long-term post-viral symptoms.
Which of the following conclusions is/are valid?
- 1. Though SARS-CoV-2 and HMPV are similar viruses with somewhat different epidemiology, the former became a pandemic because it was novel and people had not been exposed to it in the past.
- 2. The two viruses have fundamentally different impacts on human populations and should not therefore be dealt with in a similar manner.
Select the answer using the code given below.
Answer (b) & explanation
Only conclusion 2 is valid (b). Step 1: the passage stresses that SARS-CoV-2 and HMPV belong to "two very different virus families" with different seasonality, severity and affected groups. So they affect people differently and should not be handled the same way (2). Step 2: conclusion 1 calls them "similar viruses", which contradicts the passage. Step 3: so options (a), (c) and (d) fail.
Tip: one wrong word ("similar") can sink a long statement. HMPV was first identified in 2001 in the Netherlands; India reported cases in January 2025, and the Health Ministry said there was no unusual rise in illness.
Answer as per the official UPSC answer key.
The ratio of male to female workers in two companies A and B is 13 : 10 and 7 : 5, respectively. If both the companies have the same number of female workers, then what is the ratio of the total number of workers in A to those in B?
Answer (b) & explanation
The ratio of total workers is 23 : 24 (b). Step 1: the female numbers must be equal. In A, males : females = 13 : 10. In B, it is 7 : 5, which equals 14 : 10 (doubling both). Step 2: now both have 10 parts of females. A's total = 13 + 10 = 23 parts. B's total = 14 + 10 = 24 parts. Step 3: so A : B = 23 : 24. Option (a) reverses the order. Options (c) and (d) do not equalise the females first.
Tip: when one group is the same in two ratios, scale the ratios so that group has the same number of parts. Then compare totals directly.
don't add 13 + 10 and 7 + 5 directly. Equalise the common term first.
Answer as per the official UPSC answer key.
Question : If x, y and z are integers, each greater than 1, then is x a prime number?
Statement I : xy2 = 116
Statement II : xz = 261
Answer (a) & explanation
Statement I alone is enough; Statement II alone is not (a). Step 1: Statement I: xy² = 116 = 2² × 29. y is above 1 and y² must divide 116, so y² = 4, y = 2, and x = 29, a prime. So I answers "yes". Step 2: Statement II: xz = 261 = 3² × 29. With x, z above 1, x could be 3, 9, 29 or 87. Some are prime (3, 29), some are not (9, 87). So II fails. Step 3: options (b), (c) and (d) fail.
Tip: break numbers into primes first. A squared variable can only take square factors, which often leaves just one choice.
Answer as per the official UPSC answer key.
X and Y are two runners who run for the same duration of time on the same circular track. They started running at the same time in the same direction with uniform speeds. When X completed 7 rounds, Y did exactly 5. After completing 5 rounds, Y changed his direction and started running in the opposite direction with speed which is double of his earlier speed. On the other hand, X continued to run with the same speed. They stopped running when X completed exactly 21 rounds. How many times did X and Y meet after they had started and before they finally stopped?
Answer (a) & explanation
1. Phase 1, same direction, speeds 7 : 5. X gains 2 rounds, so they meet 2 times. The second meeting is at the start point, when Y turns.
2. Phase 2, opposite directions, speeds 7 and 10. X runs 14 more rounds, which takes 2 units of time. Together they cover 17 × 2 = 34 rounds, so they meet 34 times.
3. The 34th meeting is at the moment they stop, and that one is excluded. Total = 2 + 33 = 35.
read "before they finally stopped". The meeting at the stopping moment does not count.
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Answer as per the official UPSC answer key.
A train has to complete a journey of 800 km. If it meets a minor accident, its speed becomes half of the existing speed. If there is a mechanical defect, the speed becomes one-fourth of the existing speed. On its way, the train meets with a minor accident after 200 km; and 400 km thereafter, it develops a mechanical defect. Had the train developed the mechanical defect after 200 km and met the minor accident 400 km thereafter, it would have taken 4 more hours to reach its destination. What was the original speed of the train in km per hour?
Answer (a) & explanation
The original speed was 200 km/h (a). Step 1: actual journey: 200 km at v; then a minor accident halves speed: 400 km at v/2; then a defect quarters it: 200 km at v/8. Time = 200/v + 800/v + 1600/v = 2600/v. Step 2: other order: 200 km at v; defect: 400 km at v/4; accident halves again: 200 km at v/8. Time = 200/v + 1600/v + 1600/v = 3400/v. Step 3: the difference is 4 hours: 800/v = 4, so v = 200 km/h. Options (b), (c) and (d) fail.
Tip: speed changes multiply: half then a quarter gives one-eighth, in either order. Only the middle stretch differs between the two cases.
the cuts apply to the existing speed. After both events the speed is v/8 in either order. Only the middle 400 km differs.
Answer as per the official UPSC answer key.