Practice UPSC CSAT previous year questions from 2011–2026 classified underTime and Work. Review the original question, four options, correct answer and explanation for every PYQ.
12 questions • 2011–2026
P and Q walk along a circular track. They start at 5:00 a.m. from the same point in opposite directions. P walks at an average speed of 5 rounds per hour and Q walks at an average speed of 3 rounds per hour. How many times will they cross each other between 5:20 a.m. and 7:00 a.m.?
Relative speed is 8 rounds/hour; counting crossings strictly between 5:20 and 7:00 gives 13.
A set (X) of 20 pipes can fill 70% of a tank in 14 minutes. Another set (Y) of 10 pipes fills 3/8th of the tank in 6 minutes. A third set (Z) of 16 pipes can empty half of this tank in 20 minutes. If half of the pipes of set X are closed and only half of the pipes of set Y are open, and all pipes of the set Z are open, then how long will it take to fill 50% of the tank?
Net rate is 0.03125 tank/min, so 50% takes 16 minutes.
X can complete one-third of a certain work in 6 days, Y can complete one-third of the same work in 8 days and Z can complete three-fourth of the same work in 12 days. All of them work together for n days and then X and Z quit and Y alone finishes the remaining work in 8 2/3 days. What is n equal to?
Rates are 1/18,1/24,1/16; solving the remaining work after Y’s 26/3 days gives n=4.
A certain number of men can complete a piece of work in 6k days, where k is a natural number. By what percent should the number of men be increased so that the work can be completed in 5k days?
Work is constant, so men×days is constant: N×6k = N'×5k. Thus N'/N = 6/5, a 20% increase.
X, Y and Z can complete a piece of work individually in 6 hours, 8 hours and 8 hours respectively. However, only one person at a time can work in each hour and nobody can work for two consecutive hours. All are engaged to finish the work. What is the minimum amount of time that they will take to finish the work?
Use 24 units of work. X does 4 units/hour and Y/Z 3 units/hour. Alternating without consecutive hours for a person completes 21 units in six hours; X completes the final 3 units in 45 minutes, giving 6 h 45 min.
A, B, C working independently can do a piece of work in 8, 16 and 12 days respectively. A works Monday, B Tuesday, C Wednesday, A Thursday and so on. Consider: 1. The work will be finished on Thursday. 2. The work will be finished in 10 days. Which are correct?
Using rates 6,3,4 over repeating three-day cycles, completion occurs on day 11, a Thursday; only statement 1 is true.
24 men and 12 women can do a piece of work in 30 days. In how many days can 12 men and 24 women do the same piece of work?
One equation gives only the combined daily contribution of 24 men and 12 women. Without the relative efficiencies of a man and a woman, the output of 12 men and 24 women cannot be determined.
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%?
Treat the original job as 8 units: 7 units take 21 days, so 1 unit takes 3 days. A 50% increase makes the job 12 units; 5 remain, requiring 15 more days.
A person can complete 20% of work in 8 days and another person can complete 25% of the same work in 6 days. If they work together, in how many days will 40% of the work be completed?
The first rate is 2.5% per day and the second is 25/6% per day. Together they complete 20/3% per day, so 40% takes 6 days.
Ram and Shyam work on a job together for four days and complete 60% of it. Ram takes leave then and Shyam works for eight more days to complete the job. How long would Ram take to complete the entire job alone?
Together they complete 60% in 4 days, or 15% per day. Shyam completes the remaining 40% in 8 days, or 5% per day. Ram's rate is therefore 10% per day, so he needs 10 days alone.
W can do 25% of a work in 30 days, X can do 1/4 of the work in 10 days, Y can do 40% of the work in 40 days and Z can do 1/3 of the work in 13 days. Who will complete the work first?
Full-work times are W=120 days, X=40 days, Y=100 days and Z=39 days. Z therefore has the highest rate and finishes first.
Two pipes A and B can independently fill a tank completely in 20 and 30 minutes respectively. If both the pipes are opened simultaneously, how much time will they take to fill the tank completely?
Combined rate = 1/20+1/30=1/12 tank per minute, so the tank fills in 12 minutes.
Attempt questions one by one with UPSC-style marking and immediate explanations.