UPSC Prelims PYQ › Quantitative Aptitude › Time & Work, Pipes
Time & Work, Pipes — UPSC CSAT Paper II Quantitative Aptitude previous year questions
20 free solved previous year questions on Time & Work, Pipes, papers from 2013 to 2025, drawn from UPSC CSAT, UPSC CDS, covering questions of the kind UPSC asks in CSAT Paper II. Every answer key has been checked again against published sources and solved independently, and each explanation is written fresh.
Read all 20 questions with answers
- #1UPSC CSAT 2025A 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 the 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?
- A8 minutes
- B10 minutes
- C12 minutes
- D16 minutes
Answer: (D) 16 minutesExplanation
Rates per minute (as % of tank): 10 pipes of X give 2.5, 5 pipes of Y give 3.125, and Z drains 2.5.
Net filling rate = 2.5 + 3.125 - 2.5 = 3.125% per minute.
Time for 50% = 50/3.125 = 16 minutes.
Answer: option (d).Source: UPSC CSAT 2025 question; answer key checked by independent computation
- #2UPSC CSAT 2025X 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?
- A3
- B4
- C5
- D6
Answer: (B) 4Explanation
Full-work times: X 18 days, Y 24 days, Z 16 days. Combined rate = 1/18 + 1/24 + 1/16 = 23/144 per day.
Y alone does (26/3)/24 = 13/36 of the work at the end, so the team did 23/36 earlier.
n = (23/36) / (23/144) = 4.
Answer: option (b).Source: UPSC CSAT 2025 question; answer key checked by independent computation
- #3UPSC CSAT 2024A 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?
- A10%
- B(50/3)%
- C20%
- D25%
Answer: (C) 20%Explanation
Men and days are inversely proportional: N1 x 6k = N2 x 5k, so N2 = 1.2 N1.
The increase is 20%.
Answer: option (c).Source: UPSC CSAT 2024 question; answer key checked by independent computation
- #4UPSC CSAT 2024X, 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?
- A6 hours 15 minutes
- B6 hours 30 minutes
- C6 hours 45 minutes
- D7 hours
Answer: (C) 6 hours 45 minutesExplanation
Take the work as 24 units: X does 4 per hour, Y and Z do 3 each.
Best plan is X in odd hours and Y/Z alternately in even hours: after 6 hours 3 x 4 + 3 x 3 = 21 units; 6 hours cannot reach 24.
The last 3 units go to X at 4 per hour, i.e. 45 minutes, total 6 h 45 min.
Answer: option (c).Source: UPSC CSAT 2024 question; answer key checked by independent computation
- #5UPSC CSAT 2023A, B, C working independently can do a piece of work in 8, 16 and 12 days respectively. A alone works on Monday, B alone works on Tuesday, C alone works on Wednesday; A alone, again works on Thursday and so on. Consider the following statements:1. The work will be finished on Thursday.2. The work will be finished in 10 days.Which of the above statements is/are correct?
- A1 only
- B2 only
- CBoth 1 and 2
- DNeither 1 nor 2
Answer: (A) 1 onlyExplanation
Take total work 48 units: A does 6, B does 3, C does 4 per day.
Every 3 days give 13 units, so 9 days give 39 units; day 9 is a Tuesday if day 1 is Monday.
Day 10 (Wednesday, A) adds 6 to make 45; day 11 (Thursday, B) adds the last 3.
So the work ends on Thursday, in 11 days: statement 1 true, statement 2 false.
Answer: option (a).Source: UPSC CSAT 2023 question; answer key checked by independent computation
- #6UPSC CSAT 202224 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?
- A30 days
- BMore than 30 days
- CLess than 30 days or more than 30 days
- DData is inadequate to draw any conclusion
Answer: (D) Data is inadequate to draw any conclusionExplanation
Let a man's rate be m and a woman's rate be w, so 24m + 12w = 1/30.
The second group has rate 12m + 24w. This equals the first only if m = w; otherwise it is larger or smaller.
Since the relative efficiency is unknown, nothing definite can be said.
Answer: option (d).Source: UPSC CSAT 2022 question; answer key checked by independent computation
- #7UPSC CSAT 2021A 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%?
- A24
- B21
- C18
- D15
Answer: (D) 15Explanation
Full job takes 21 x 8/7 = 24 days.
With 50% more work, total time = 24 x 1.5 = 36 days.
Already worked 21 days, so 36 - 21 = 15 more days.
Answer: option (d).Source: UPSC CSAT 2021 question; answer key checked by independent computation
- #8UPSC CSAT 2020A person X can complete 20% of work in 8 days and another person Y 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?
- A6
- B8
- C10
- D12
Answer: (A) 6Explanation
X's rate = 1/40 per day (full work in 40 days); Y's rate = 1/24 per day.
Together = 1/40 + 1/24 = 1/15 per day, i.e. the whole job in 15 days.
40% of the work takes 0.4 x 15 = 6 days.
Answer: option (a).Source: UPSC CSAT 2020 question; answer key checked by independent computation
- #9UPSC CSAT 2016Ram 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?
- A6 days
- B8 days
- C10 days
- D11 days
Answer: (C) 10 daysExplanation
Shyam does the remaining 40% in 8 days, i.e. 5% per day.
Together they do 60%/4 = 15% per day, so Ram does 10% per day.
Ram alone needs 100/10 = 10 days.
Answer: option (c).Source: UPSC CSAT 2016 question; answer key checked by independent computation
- #10UPSC CSAT 2016W 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?
- AW
- BX
- CY
- DZ
Answer: (D) ZExplanation
Full-work times: W = 120 days, X = 40 days, Y = 100 days, Z = 39 days.
Z needs the fewest days.
Answer: option (d).Source: UPSC CSAT 2016 question; answer key checked by independent computation
- #11UPSC CSAT 2015Two 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?
- A10 minutes
- B12 minutes
- C15 minutes
- D25 minutes
Answer: (B) 12 minutesExplanation
Combined rate = 1/20 + 1/30 = 5/60 = 1/12 tank per minute.
Time = 12 minutes.
Answer: option (b).Source: UPSC CSAT 2015 question; answer key checked by independent computation
- #12UPSC CSAT 2013In a garrison, there was food for 1000 soldiers for one month. After 10 days, 1000 more soldiers joined the garrison. How long would the soldiers be able to carry on with the remaining food?
- A25 days
- B20 days
- C15 days
- D10 days
Answer: (D) 10 daysExplanation
Food is 1000 x 30 = 30,000 soldier-days (taking a month as 30 days). In 10 days 10,000 are used, leaving 20,000.
With 2000 soldiers, 20,000/2000 = 10 days.
Answer: option (d).Source: UPSC CSAT 2013 question; answer key checked by independent computation
- #13UPSC CDS 2023If A and B finish a work in 10 days, B and C can finish the same work in 12 days, C and A can finish the same work in 15 days; then in how many days can A, B and C together finish half of the work?
- A8 days
- B5 days
- C4 days
- D3 days
Answer: (C) 4 daysExplanation
Take total work as 60 units. A+B = 6, B+C = 5, C+A = 4 units per day.
Adding, 2(A+B+C) = 15, so A+B+C = 7.5 units per day.
Half the work = 30 units, so time = 30/7.5 = 4 days.
Answer: option (c).Source: UPSC CDS 2023 question; answer key checked by independent computation
- #14UPSC CDS 2023Three persons A, B and C together can do a piece of work in 36 days. A and B together can do five times as much work as C alone; B and C together can do as much work as A alone. If A and C together can do n times as much work as B alone, then what is the value of n?
- A1.5
- B2
- C2.5
- D3
Answer: (B) 2Explanation
Rates: A+B+C = 1/36, A+B = 5C gives 6C = 1/36, so C = 1/216.
B+C = A gives 2A = 1/36, so A = 1/72, and B = 1/72 - 1/216 = 1/108.
A + C = 1/54, which is 2 times B (1/108).
Answer: option (b).Source: UPSC CDS 2023 question; answer key checked by independent computation
- #15UPSC CDS 2023A can do a certain work at twice the speed of B. Further, B can do the same work at 1.5 times the speed of C. All of them together can finish the work in 12 days. In how many days can C alone finish the work?
- A36 days
- B45 days
- C60 days
- D66 days
Answer: (D) 66 daysExplanation
Let C's speed be 1 unit; then B = 1.5 and A = 3, total 5.5 units per day.
Work = 5.5 x 12 = 66 units.
C alone takes 66/1 = 66 days.
Answer: option (d).Source: UPSC CDS 2023 question; answer key checked by independent computation
- #16UPSC CDS 2023If 17 women and 24 men can do a piece of work in 5 days and 12 women and 23 men can do it in 6 days, then which one of the following is correct?
- AEfficiency of 13 women = Efficiency of 18 men
- BEfficiency of 11 women = Efficiency of 16 men
- CEfficiency of 13 women = Efficiency of 17 men
- DEfficiency of 11 women = Efficiency of 15 men
Answer: (A) Efficiency of 13 women = Efficiency of 18 menExplanation
Total work is the same: 5(17W + 24M) = 6(12W + 23M).
85W + 120M = 72W + 138M, which gives 13W = 18M.
Answer: option (a).Source: UPSC CDS 2023 question; answer key checked by independent computation
- #17UPSC CDS 2023Three taps A, B and C together can fill a tank in 6 hours. Tap C alone can fill the tank in 12 hours. To fill the tank, when it is empty, all the three taps are started together. After working t hours, tap C is closed and the tank is filled in 8 more hours. What is t equal to?
- A1
- B2
- C4
- D6
Answer: (B) 2Explanation
A + B together fill 1/6 - 1/12 = 1/12 of the tank per hour.
In the last 8 hours they fill 8/12 = 2/3 of the tank.
So the first t hours must fill 1/3: t/6 = 1/3, hence t = 2.
Answer: option (b).Source: UPSC CDS 2023 question; answer key checked by independent computation
- #18UPSC CDS 2023A, B and C can complete a work in x, 1.5x and 2x days respectively. If they complete the work together, in what ratio should they be paid?
- A2:3:4
- B6:4:3
- C3:2:1
- D4:3:2
Answer: (B) 6:4:3Explanation
Payment is in the ratio of work done, i.e. of daily rates when all work for the same time.
Rates are 1/x : 1/(1.5x) : 1/(2x) = 1 : 2/3 : 1/2.
Multiplying by 6 gives 6 : 4 : 3.
Answer: option (b).Source: UPSC CDS 2023 question; answer key checked by independent computation
- #19UPSC CDS 2022X and Y can do a piece of work in 45 days and 40 days respectively. They begin to work together, but X leaves after n days and then Y completes the remaining work in 23 days. What is n equal to?
- A8
- B9
- C10
- D12
Answer: (B) 9Explanation
Together they do 1/45 + 1/40 = 17/360 per day.
Y alone does 23/40 in 23 days, so the joint work is 1 - 23/40 = 17/40.
n x 17/360 = 17/40 gives n = 9.
Answer: option (b).Source: UPSC CDS 2022 question; answer key checked by independent computation
- #20UPSC CDS 2022480 persons working 10 hours per day complete one-fourth of a work in 10 days. How many additional persons are to be employed in order to complete the remaining work in 20 days, working 8 hours per day?
- A400
- B420
- C480
- D500
Answer: (B) 420Explanation
One-fourth of the work = 480 x 10 x 10 = 48,000 man-hours, so the remaining three-fourths = 144,000 man-hours.
Persons needed = 144000/(20 x 8) = 900.
Additional persons = 900 - 480 = 420.
Answer: option (b).Source: UPSC CDS 2022 question; answer key checked by independent computation
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