Quantitative Aptitude

Pipes and Cisterns

69 Questions

Pipes and cisterns problems test your understanding of inlet and outlet rates alongside time management. These questions are a staple in quantitative aptitude sections for SSC, banking, and railways. Mastering filling and emptying concepts is essential for scoring well.

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Pipes and Cisterns Questions

Multiple choice general knowledge math & puzzles

A tap can fill the tank in 16 minutes and another can empty it in 8 minutes. If the tank is already half full and both the taps are opened together, the tank will be:

  1. filled in 12 min

  2. emptied in 12 min

  3. filled in 8 min

  4. emptied in 8 min
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Fill tap rate: 1/16 tank per minute. Empty tap rate: 1/8 tank per minute. Net rate when both open: 1/16 - 1/8 = 1/16 - 2/16 = -1/16 tank per minute (negative means emptying). Tank is half full (1/2). Time to empty: (1/2) ÷ (1/16) = (1/2) × 16 = 8 minutes.

Multiple choice general knowledge math & puzzles

One pipe can fill a tank three times as fast as another pipe. If together the two pipes can fill the tank in 36 minutes, then the slower pipe alone will be able to fill the tank in:

  1. 81 min

  2. 108 min

  3. 144 min

  4. 192 min
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Let the slower pipe's rate be x. The faster pipe's rate is 3x. Combined rate is 4x. In 36 minutes, they fill 4x * 36 = 144x units. The slower pipe alone takes (144x / x) = 144 minutes.

Multiple choice general knowledge math & puzzles

Faucet A fills a tank in 3 hours, and faucet B drains the tank in 9 hours. What fraction of the tank will be filled, if both the faucets are kept running for 1½ hours, and the tank is originally empty?

  1. 1/4

  2. 1/3

  3. 1/2

  4. 2/3

  5. 3/4
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Faucet A fills at 1/3 tank per hour, faucet B drains at 1/9 tank per hour. Net fill rate = 1/3 - 1/9 = 2/9 tank per hour. In 1.5 hours: 2/9 × 3/2 = 1/3 tank. Option B is correct.

Multiple choice general knowledge math & puzzles

Tap A and Tap B can fill a tank in 10 hours and 20 hours respectively. Tap C can empty the tank in 30 hours. Tap A and Tap B are opened for 5 hours. After that Tap C is opened. Find the total time taken in filling the tank upto 87.5% of its volume.

  1. 50/7 hours

  2. 85/14 hours

  3. 100/7 hours

  4. 95/14 hours
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Tap A fills 1/10 per hour, Tap B fills 1/20 per hour. In first 5 hours, A+B fill 5*(1/10+1/20) = 3/4 of tank. Remaining 13.5% is 27/200. With A+B+C running, net rate is 5/12 per hour. Time = (27/200)/(5/12) = 81/500 hours. Total = 5 + 81/500 = 85/14 hours.

Multiple choice general knowledge math & puzzles

Pipe A can fill a tank in 'a' hours. On account of a leak at the bottom of the tank it takes thrice as long to fill the tank. How long will the leak at the bottom of the tank take to empty a full tank, when pipe A is kept closed?

  1. (2/3)a hours

  2. (3/2)a hours

  3. 3/4)a hours

  4. (5/3) a hours
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Pipe A fills in a hours, so rate = 1/a tank per hour. With the leak, effective rate = 1/(3a). Let leak rate = -1/x (negative because it empties). Then 1/a - 1/x = 1/(3a). Solving: 1/x = 1/a - 1/(3a) = 2/(3a), so x = (3/2)a hours.

Multiple choice general knowledge

How much water is used to flush the average toilet?

  1. 2 gallons

  2. 1 gallon

  3. 3 gallons

  4. 4 gallons

  5. <1gallon
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Traditional toilets use approximately 3-5 gallons per flush, with 3 gallons being the standard average for older models. Modern low-flow toilets use less, but the question asks about the average toilet.

Multiple choice general knowledge math & puzzles

A swimming pool has four faucets. The first can fill the entire pool with water in two days, the second – in three days, the third – in four days, and the last one can fill the pool in 6 hours. How long will it take(approximately) to fill the pool using all 4 faucets together?

  1. 5 hr 15 min

  2. 6 hr

  3. 4 hr 43 min

  4. 3 hr
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Convert all rates to per-hour basis. First: 1 pool/48 hours = 1/48 pool/hour. Second: 1/72 pool/hour. Third: 1/96 pool/hour. Fourth: 1/6 pool/hour. Combined rate: 1/48 + 1/72 + 1/96 + 1/6 = (6+4+3+48)/288 = 61/288 pool/hour. Time = 1 / (61/288) = 288/61 hours ≈ 4.72 hours = 4 hours + 0.72×60 min = 4 hours 43.2 minutes, which rounds to approximately 4 hr 43 min.

Multiple choice general knowledge math & puzzles

Pipe A can fill in 20 minutes and Pipe B in 30 mins and Pipe C can empty the same in 40 mins.If all of them work together, find the time taken to fill the tank

  1. 20 mins

  2. 8 mins

  3. 17 1/7 mins

  4. 171/6 mins
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Combined rate = 1/20 + 1/30 - 1/40 = 6/120 + 4/120 - 3/120 = 7/120 tank per minute. Time = 120/7 = 17 1/7 minutes. Pipe C empties, so its contribution is negative. The net rate determines how quickly the tank fills.

Multiple choice general knowledge math & puzzles

There is a water-cask with three different water-taps. With the smallest tap the water-cask can be filled in 20 minutes. With middle the tap the water-cask can be filled in 12 minutes. With the largest tap the water-cask can be filled in 5 minutes. The Question: How long does it take to fill the water-cask with the three taps together?

  1. 3.5 min

  2. 2.5 min

  3. 4 min

  4. 3 min
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Combined rate = 1/20 + 1/12 + 1/5. Using a common denominator of 60: (3 + 5 + 12) / 60 = 20 / 60 = 1/3. The time taken is the reciprocal of the rate, which is 3 minutes.

Multiple choice softskills communication

Pipe A can fill in 20 minutes and Pipe B in 30 mins and Pipe C can empty the same in 40 mins. If all of them work together, find the time taken to fill the tank ?

  1. 17 1/7 mins

  2. 20 mins

  3. 8 mins

  4. None of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The combined rate is 1/20 + 1/30 - 1/40. Finding a common denominator (120), we get (6 + 4 - 3)/120 = 7/120. The time taken is the reciprocal, 120/7, which equals 17 1/7 minutes. The other options do not match the result of this rate calculation.