Quantitative Aptitude

Pipes and Cisterns

535 Questions
All Delayed opening or closing 106 Combined pipes and the LCM shortcut 77 Find unknown pipe time 64 Efficiency ratios and faster-pipe relations 61 Flow rates based on pipe diameter 50 Leaks and reverse-rate questions 50 Actual capacity and pump-rate equations 44 Partial filling or emptying condition 44 Alternating pipes and changing phases 39

Pipes and Cisterns Questions

Multiple choice

A filling pipe can fill a empty tank in 15 hrs while draining pipe can empty the same tank in 25hrs.If a system of n pipes including filling and draining pipes an fill an empty pool in 5 hrs. And if n is neither less than nor Greater than 43 , then which of the following is true

  1. more than 20 filling pipes were installed

  2. Less than 19 filling pipes were installed

  3. Number of draining pipes was 7 more than the filling pipes

  4. More than one is true
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Interpreting the condition as n = 43, let f be the number of filling pipes and d the number of draining pipes. Solving f + d = 43 and f/15 - d/25 = 1/5 gives f = 18 and d = 25. Thus fewer than 19 filling pipes were installed, and the draining pipes were 7 more than the filling pipes, so more than one statement is true.

Multiple choice

Three pipes can fill a tank in 15, 20, and 25 hours respectively. Two other pipes can empty it in 30 and 40 hours respectively. If all the pipes are opened together, in how many hours will the empty tank be filled (approximately)?

  1. 9.8 hours

  2. 10.2 hours

  3. 10.5 hours

  4. 11.4 hours
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Net rate = 1/15 + 1/20 + 1/25 - 1/30 - 1/40. Common denominator = 600. Rate = (40 + 30 + 24 - 20 - 15) / 600 = 59 / 600. Time = 600 / 59 approx 10.17 hours.

Multiple choice

A cistern of dimensions 2.4 yards × 2.0 yards × 1.5 yards takes 2 hrs. 24 min. to get filled with water. The rate at which water flows into the cistern is

  1. 2332.8 cubic inches/min

  2. 194.4 cubic feet/hr

  3. 7.2 cubic yards/hr

  4. 17.28 cubic yards/hr

  5. 233.2 cubic yards/hr
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Volume = 2.4 * 2.0 * 1.5 = 7.2 cubic yards. 7.2 cubic yards = 7.2 * 46656 cubic inches = 335923.2 cubic inches. Time = 2 hrs 24 min = 144 minutes. Rate = 335923.2 / 144 = 2332.8 cubic inches/min.

Multiple choice

Time taken by two pipes A and B to fill a cistern is 28 hours and 32 hours, respectively. At a particular instant of time, we open both pipes to fill the cistern. There is a little hole at the bottom of the cistern. The pipes took 64 minutes more. After completely filling the cistern, how much time would the hole take to empty the cistern?

  1. 112 hours

  2. 224 hours

  3. 118 hours

  4. 236 hours

  5. None of the above
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Rate A = 1/28, Rate B = 1/32. Combined rate = 1/28 + 1/32 = (8+7)/224 = 15/224. Time = 224/15 hours = 14.933 hours = 896 minutes. With hole, time = 896 + 64 = 960 minutes = 16 hours. Combined rate - hole = 1/16. Hole rate = 15/224 - 1/16 = (15-14)/224 = 1/224. Hole takes 224 hours.

Multiple choice

Two pipes X and Y can fill an empty tank in 16 and 24 hours respectively. Ravi opens these two pipes simultaneously. After 8/3 hours he comes back and sees that there was a leak in the tank. He stops the leakage and thus tank took 48/5 hours to be filled completely after closing the leak. In what time leakage will empty the filled tank?

  1. 6.9 hrs

  2. 9.6 hrs

  3. 8.4 hrs

  4. 9.4 hrs
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The combined filling rate of pipes X and Y is 1/16 + 1/24 = 5/48 of the tank per hour. After the leak is closed, the tank takes 48/5 hours to fill completely, which means X and Y filled (5/48) * (48/5) = 1 (the entire tank) during this time. This implies that no water accumulated during the first 8/3 hours because the leak rate was exactly equal to the combined filling rate of 5/48. Thus, the leak alone can empty the full tank in 1 / (5/48) = 9.6 hours.

Multiple choice

The time taken by pipe A to fill a water tank is 32 minutes. Pipes B and C can together fill the water tank in 12 minutes. If the water comes twice as fast as pipe A through pipe C, then find the time taken by pipes A and B together to fill the water tank.

  1. 19.6 minutes

  2. 19.2 minutes

  3. 18.8 minutes

  4. 18.4 minutes

  5. 17.2 minutes
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Pipe A fills 1/32 of the tank per minute, and pipes B and C together fill 1/12 per minute. Since C works twice as fast as A, its rate is 1/16, so B's rate is 1/48. Thus A and B together fill 5/96 of the tank per minute, taking 19.2 minutes.

Multiple choice

Directions : Answer the question independently. Water is being poured into a tank at a constant rate using an inlet pipe. There are a number of outlet pipes of equal capacities attached to the tank. Initially the tank is full and all the inlet and outlet pipes are open. It is observed 10 outlet pipes empty the tank in 12 hrs, while 15 pipes empty the tank in 6 hrs. In how much time (in hours) would 25 pipes empty the tank, if the tank is initially full?

  1. 2.5 hrs

  2. 4 hrs

  3. 3 hrs

  4. 1/3 hrs
Reveal answer Fill a bubble to check yourself
C Correct answer
Multiple choice

Directions: Answer the question independently. A tank has three pipes—Pipe A, Pipe B and Pipe C attached. Pipe A and Pipe C alone can fill the tank completely in 4 hours and 8 hours respectively. Pipe B can empty the tank in 6 hours. Initially the tank is empty. The three pipes are operated in the following sequence. In the first hour, only pipe A is opened. In the second hour, pipes A and B are opened. In the third hour, only pipe B is opened. In the fourth hour, pipes B and C are opened. In the fifth hour, only pipe C is opened. This cycle of 5 hours is repeated. After how many hours will the tank be completely filled for the first time?

  1. 1.5 hours

  2. 18 hours

  3. 20 hours

  4. 16 hours
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Rates: A = +1/4, B = -1/6, C = +1/8. Cycle (5 hours): Hr 1: +1/4. Hr 2: +1/4 - 1/6 = +1/12. Hr 3: -1/6. Hr 4: -1/6 + 1/8 = -1/24. Hr 5: +1/8. Net per cycle = 1/4 + 1/12 - 1/6 - 1/24 + 1/8 = (6+2-4-1+3)/24 = 6/24 = 1/4. After 3 cycles (15 hours), tank is 3/4 full. Hr 16: +1/4. Total = 1. Tank is full at 16 hours.

Multiple choice

Directions: Answer the questions independently of each other. Pipe A, B and C are kept open and together fill a tank in t minutes. Pipe A is kept open throughout, pipe B is kept open for the first 10 minutes and then closed. Two minutes after pipe B is closed, pipe C is opened and is kept open till the tank is full. Each pipe fills an equal share of the tank. Furthermore, it is known that if pipe A and B are kept open continuously, the tank would be filled completely in t minutes. How long will C alone take to fill the tank?

  1. 18

  2. 36

  3. 27

  4. 24
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Let the total work be 1 unit. A, B, C fill it in t minutes together, so rate A+B+C = 1/t. A and B together fill in t minutes, so rate A+B = 1/t. This implies C's rate is 0, which contradicts the problem. Re-reading: 'Each pipe fills an equal share of the tank'. This means each fills 1/3 of the tank. A works for the whole time T_total. B works for 10 mins. C works for (T_total - 12) mins. A's rate = (1/3) / T_total. B's rate = (1/3) / 10. C's rate = (1/3) / (T_total - 12). Since A+B fill in t minutes, (1/3T_total + 1/30) * t = 1. Solving these leads to T_total = 36. C's time = 36 - 12 = 24.

Multiple choice

An empty tank needs to be filled with water using three pipes A, B and C. Pipes A and B alone can fill the tank in 16 hours and 20 hours, respectively. If the pipes A and B are opened in alternate hours along with C, i.e., in the first hour, pipes A and B fill the tank, in the second hour pipes B and C fill the tank and so on, then 90% of the tank is filled in 11 hours. How long, in hours, will pipe C alone take to fill the tank?

  1. 60

  2. 32

  3. 24

  4. 40
Reveal answer Fill a bubble to check yourself
D Correct answer
Multiple choice

Pipes A and C are fill pipes while Pipe B is a drain pipe of a tank. Pipe B empties the full tank in one hour less than the time taken by Pipe A to fill the empty tank. When pipes A, B and C are turned on together, the empty tank is filled in two hours. If pipes B and C are turned on together when the tank is empty and Pipe B is turned off after one hour, then Pipe C takes another one hour and 15 minutes to fill the remaining tank. If Pipe A can fill the empty tank in less than five hours, then the time taken, in minutes, by Pipe C to fill the empty tank is

  1. 90

  2. 60

  3. 120

  4. 75
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Let A, B, and C be the rates of the pipes. Given 1/A + 1/C - 1/B = 1/2. Also, B = A - 1. Using the second condition, (1/C - 1/B) * 1 + 1/C * 1.25 = 1. Solving these equations leads to the rate of C, which results in a fill time of 90 minutes.