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

Pipe A takes 10 minutes less than pipe B to fill a petrol tank, but takes 10 minutes and 25 seconds more than the two together. Find the time taken by pipe A alone to fill the petrol tank.

  1. 20 minutes

  2. 25 minutes

  3. 35 minutes

  4. 40 minutes
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let A take x minutes, B take x+10 minutes. Together they take 1/(1/x + 1/(x+10)) = x(x+10)/(2x+10). Given x = x(x+10)/(2x+10) + 10.416 (10m 25s). Solving this leads to x = 25.

Multiple choice

Directions: Solve the following question and mark the best possible option. A tank has an inlet pipe and an outlet pipe. If the outlet pipe is closed then the inlet pipe fills the empty tank in 8 hours. If the outlet pipe is open then the inlet pipe fills the empty tank in 10 hours. If only the outlet pipe is open then in how many hours the full tank becomes half-full?

  1. 20

  2. 30

  3. 40

  4. 45
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Let inlet rate be I and outlet rate be O. Given 1/I = 8, so I = 1/8. With outlet open, net rate is 1/10, so I - O = 1/10. Substituting I, 1/8 - O = 1/10, so O = 1/8 - 1/10 = 1/40. Time for outlet to empty full tank is 40 hours. Time for half-full is 40/2 = 20 hours.

Multiple choice

In the dairy technology lab at a university, a technician fills a holding tank of capacity 50 litres by using 3 different pipes. The rate of flow through each pipe is equal to 1 litre/min. The 1st pipe pours milk only, the 2nd pipe pours water only and the 3rd pipe pours a mixture of milk and water, in which the ratio of milk to water is 2 : 3. At any given instance, only 1 of the 3 pipes is opened. Each of the pipes is opened to fill its contents into the holding tank for exactly 5 minutes after which it is replaced by one of the other 2 pipes. The ratio of milk to water in the tank after 50 minutes cannot be

  1. 2 : 3

  2. 9 : 16

  3. 6 : 19

  4. 21 : 29
Reveal answer Fill a bubble to check yourself
C Correct answer
Multiple choice

The mixing tank of an effluent treatment plant (ETP) is in the form a right circular cylinder with a uniform cross section. It has an adjustable outlet pipe that can be attached to the tank at any height desired. The outlet pipe drains water out of the tank via a pump at a constant rate irrespective of the height it is attached at. The tank is filled at a constant rate using another inlet pipe. If the outlet pipe is attached at half the height of the tank, the tank which is initially empty gets filled in 18 hours. If the outlet pipe is attached at height equal to 2/3rd the height of the tank, the tank which is initially empty gets filed in 16 hours. In how many hours will the tank, that is initially empty, be completely filled, if the outlet pipe is not attached to the tank?

  1. 8

  2. 9

  3. 12

  4. 14
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Let the filling-only time be p and the effective filling time above the outlet be q. The two cases give p + q = 36 and 2p + q = 48, so p = 12 hours. With no outlet attached, the tank fills in 12 hours.

Multiple choice

Pipes A, B and C can fill a tank in 30 h, 40 h and 60 h, respectively. Pipes A, B and C are opened at 7 a.m., 8 a.m. and 10 a.m., respectively on the same day. When will the tank be full?

  1. 10 : 00 pm

  2. 10 : 20 pm

  3. 9 : 20 pm

  4. 9 : 40 pm
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Let the tank capacity be 120 units. A fills 4 u/h, B fills 3 u/h, C fills 2 u/h. By 10 a.m., A has worked 3 hours (12 units) and B has worked 2 hours (6 units). Total filled = 18 units. Remaining = 102 units. Combined rate = 4+3+2 = 9 u/h. Time = 102/9 = 11 hours 20 minutes. 10 a.m. + 11h 20m = 9:20 p.m.

Multiple choice

A tank can be filled by three pipes in 20 min, 30 min and 60 min, respectively. When the tank is empty, the three pipes are opened. After 4 min, the first pipe stops working. After how much time will the 2nd and 3rd pipes fill the tank?

  1. 6 min

  2. 8 min

  3. 10 min

  4. 12 min

  5. None of these
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The pipes fill 1/20, 1/30, and 1/60 of the tank per minute. In 4 minutes, the three pipes together fill 4 * (1/20 + 1/30 + 1/60) = 4 * (3+2+1)/60 = 4 * 6/60 = 2/5 of the tank. The remaining 3/5 of the tank is filled by the 2nd and 3rd pipes at a combined rate of (1/30 + 1/60) = 3/60 = 1/20 per minute, taking (3/5) / (1/20) = 12 minutes.

Multiple choice

A cistern can be filled by pipes A and B in 4 hours and 6 hours, respectively. When full, the cistern can be emptied by a pipe C in 8 hours. If all the taps are turned on at the same time, the cistern will be full in

  1. 3 hours 18 minutes

  2. 3 hours 26 minutes

  3. 3 hours 42 minutes

  4. 3 hours 48 minutes

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

The rates are A=1/4, B=1/6, and C=-1/8. Combined rate = 1/4 + 1/6 - 1/8 = (6+4-3)/24 = 7/24. Time to fill = 24/7 hours, which is 3 hours and 3/7 hours. 3/7 of 60 minutes is approximately 25.7 minutes.