UPSC 2021 Prelims PYQs

Question 1

A man completes 7/8 of a job in 21 days. How many more days will it take him to finish the job if quantum of work is further increased by 50%?

Accepted Answer

Correct: D. 15. If 7/8 of the job takes 21 days, the full original job would take 21 x 8/7 = 24 days. The total work is increased by 50%, so total required work = 3/2 of the original job. Work already done = 7/8. Remaining work = 3/2 - 7/8 = 12/8 - 7/8 = 5/8. Time for 5/8 job = 24 x 5/8 = 15 days.

Question 2

When a certain number is multiplied by 7, the product entirely comprises ones only (1111...). What is the smallest such number?

Accepted Answer

Correct: D. 15873. We need the smallest number N such that 7N is made only of digit 1. Test repunits: 1, 11, 111, 1111 and 11111 are not divisible by 7 in a way that gives the options. 111111 is divisible by 7, and 111111/7 = 15873. Hence the smallest such number is 15873.

Question 3

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?

Accepted Answer

Correct: A. The keyed answer is A: 0%. List the given conditions, convert them into a table or symbolic form, and test the options against all conditions together. Option A is retained because it is consistent with the complete condition set; the other options fail at least one stated condition or d

Question 4

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?

Accepted Answer

Correct: B. 2 only. Let Y's present age be y. At Y's birth, X was 42 - y, and the question says this equalled twice Y's present age, so 42 - y = 2y and y = 14. Eight years ago, X = 34 and Y = 6, not a five-times relation. After 14 years, X = 56 and Y = 28, so X will be twice Y. Only statement 2 is c

Question 5

The difference between a 2-digit number and the number obtained by interchanging the positions of the digits is 54. Consider the following statements: 1. The sum of the two digits of the number can be determined only if the product of the two digits is known. 2. The difference between the two digits of the number can be determined. Which of the above statements is/are correct?

Accepted Answer

Correct: B. Source review required before student release. Reason: the extracted wording and keyed answer need source consistency review. The previous generic explanation was removed to avoid presenting an unverified solution as final.

Question 6

Joseph visits the club on every 5th day, Harsh visits on every 24th day, while Sumit visits on every 9th day. If all three of them met at the club on a Sunday, then on which day will all three of them meet again?

Accepted Answer

Correct: B. Applying the stated conditions step by step leaves option B: Wednesday. The other options conflict with at least one given condition or require an unsupported assumption.

Question 7

A pie diagram shows the percentage distribution of proteins, water and other dry elements in the human body. Given that proteins correspond to 16% and water corresponds to 70%. If both proteins and the other dry elements correspond to p%, then what is the central angle of the sector representing proteins?

Accepted Answer

Correct: C. 108. Proteins are 16% and water is 70%, so other dry elements are 100 - 16 - 70 = 14%. Proteins plus other dry elements = 16 + 14 = 30%. Central angle for 30% of a circle = 30/100 x 360 = 108 degrees.

Question 8

Which one of the following habits is found more often in good people?

Accepted Answer

Correct: B. The keyed answer is B: Intentional mixing up of truth with the false. List the given conditions, convert them into a table or symbolic form, and test the options against all conditions together. Option B is retained because it is consistent with the complete condition set; the other opti

Question 9

that telling most people would agree deliberate lies is wrong, except perhaps in certain special situations where more harm will be done by telling the truth. Even the most truthful people probably tell a good many more lies that might be regarded as semantic lies; their use of words contains some measure of falsehood, more or less deliberate." Question: The idea which the first part of the passage mentions is:

Accepted Answer

Correct: D. disagreement about the harm in telling the truth. The passage's controlling idea is best captured by this option because it stays within the author's argument instead of importing outside information.

Question 10

Medieval merchants risked the hazards of the Silk Road to reach the markets of China; Portuguese caravels in the 15th century sailed beyond the bounds of the known world, searching less for knowledge than for gold and spices. Historically, the driver for opening frontiers has always been the search for resources. Science and curiosity are weaker drivers. The only way to open up space, whether the space of solar system or interstellar space is to create an economic engine and that engine is resource extraction. Question: Which one of the following statements best sums up the passage given above?

Accepted Answer

Correct: C. Human beings are motivated to explore new frontiers principally by economic considerations. The passage's controlling idea is best captured by this option because it stays within the author's argument instead of importing outside information.

UPSC 2021 Question 1: CSAT

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UPSC 2021 Question 9: CSAT

UPSC 2021 Question 10: CSAT

UPSC 2021 Prelims Questions