Pipes and Cisterns Practice Test Questions - Aptitude -- Free Practice

Question 1

A water tank has two pipes to fill water in it. One of the pipes fills water at the rate of 100 litres per hour. The tank is filled by the other pipe in 6 hours and by both pipes together in 4.2 hours. What is the capacity of the tank in litres ?

A

860 litre✓✗

B

980 litre✓✗

C

1120 litre✓✗

D

1400 litre✓✗

Explanation

Let the capacity be C litres. The second pipe fills the tank in 6 hours, so its rate is C6 per hour.
Both together: (100 + C6) × 4.2 = C, so 420 + 0.7C = C.
0.3C = 420, so C = 1400 litres.

Question 2

A cistern has two taps attached to it. Tap B can empty the cistern in 45 minutes. But Tap A can fill the cistern in just 30 minutes. Rohit started both taps unknowingly but realized his mistake after 30 minutes. He immediately closed Tap B. Now after this, in how much time will the cistern be filled?

A

30 minutes✓✗

B

45 minutes✓✗

C

15 minutes✓✗

D

20 minutes✓✗

Explanation

With both taps open, the work in one minute = 130 - 145 = 190. In 30 minutes, 3090 = 13 of the cistern is filled.
The remaining 23 is filled by Tap A alone in 23 × 30 = 20 minutes.

Question 3

There is a leak at the bottom of a cistern. Due to this it takes 8 hours to fill the cistern. Had there not been a leak, it would take one hour less to fill the cistern. How much time does it take for the leak to completely empty the cistern?

A

48 hours✓✗

B

55(13) hours✓✗

C

56 hours✓✗

D

15 hours✓✗

Explanation

The filling rate without the leak = 17 per hour and with the leak = 18 per hour.
The leak's rate = 17 - 18 = 156 per hour.
The leak empties the full cistern in 56 hours.

Question 4

A cistern is normally filled with water in 10 hours but takes 5 hours longer to fill because of a leak in its bottom. If the cistern is full, the leak will empty the cistern in

A

20 hours✓✗

B

40 hours✓✗

C

50 hours✓✗

D

30 hours✓✗

Explanation

The filling rate = 110 per hour and with the leak = 115 per hour.
The leak's rate = 110 - 115 = 130 per hour.
The leak empties the full cistern in 30 hours.

Question 5

A tap having diameter 'd' can empty a tank in 84 min. How long another tap having diameter '2d' take to empty the same tank?

A

21 minutes✓✗

B

42 minutes✓✗

C

168 minutes✓✗

D

28 minutes✓✗

Explanation

The flow through a tap is proportional to the area of its cross-section, which is proportional to the square of the diameter.
A tap of diameter 2d has an area 4 times that of a tap of diameter d, so it empties the tank in 844 = 21 minutes.

Question 6

Two pipes M and N can fill a tank in 22.5 and 15 minutes, respectively. If both the pipes are opened simultaneously, after how much time should N be closed so that the tank is full in 18 minutes?

A

4 minutes✓✗

B

3 minutes✓✗

C

4.5 minutes✓✗

D

2.5 minutes✓✗

Explanation

Pipe M fills 122.5 = 245 and pipe N fills 115 of the tank per minute. M works for all 18 minutes and fills 18 × 245 = 45.
The remaining 15 is filled by N in 15 × 15 = 3 minutes.
N should be closed after 3 minutes.

Question 7

Pipe P can fill a tank in 38 hours. Pipe Q alone can fill it in 19 hours. Pipe R can empty the full tank in 133 hours. If all the pipes are opened together, how much time will be needed to make the tank full?

A

28 hours✓✗

B

95 hours✓✗

C

19 hours✓✗

D

14 hours✓✗

Explanation

The pipes fill 138, 119 and empty 1133 of the tank per hour.
Net rate = 138 + 119 - 1133 = 7 + 14 - 2266 = 19266 = 114.
The tank fills in 14 hours.

Question 8

3 pipes have diameters 2 cms, 3 cms and 4 cms. The ratio of water flowing through them is equal to ratio of the square of their diameters. The biggest pipe when open alone, can fill the entire pool in just 126 minutes. When all the pipes are opened together, the pool would be filled in how much time?

A

201629 minutes✓✗

B

2111126 minutes✓✗

C

21563 minutes✓✗

D

155 minutes✓✗

Explanation

The flows are in the ratio of the squares of the diameters, 4 : 9 : 16.
The biggest pipe (16 parts) fills the pool in 126 minutes, so 1 part fills 116 × 126 = 12016 of the pool per minute.
All three fill (4 + 9 + 16) = 29 parts per minute = 292016.
Time = 201629 minutes.

Question 9

Two pipes M and N can fill a tank in 22 hours and 33 hours respectively. In how much time will the tank be full, if both the pipes are opened simultaneously?

A

18 hours✓✗

B

1922 hours✓✗

C

1(111) hours✓✗

D

13(15) hours✓✗

Explanation

Pipe M fills 122 and pipe N fills 133 of the tank per hour.
Together = 366 + 266 = 566.
Time = 665 = 1315 hours.

Question 10

Pipe P can fill a tank in 4 hours, pipe Q in 8 hours and pipe R in 24 hours. If all the pipes are open, in how many hours will the tank be filled?

A

2 hours✓✗

B

2.4 hours✓✗

C

3 hours✓✗

D

3.5 hours✓✗

Explanation

The pipes fill 14, 18 and 124 of the tank per hour.
Together = 6 + 3 + 124 = 1024.
Time = 2410 = 2.4 hours.

Question 11

If a pipe can fill a tank in 6 hours, find the part of tank it fills in one hour.

A

16✓✗

B

23✓✗

C

12✓✗

D

None of these✓✗

Explanation

The pipe fills the tank in 6 hours, so in one hour it fills 16 of the tank.

Question 12

A leak at the bottom of the tank can empty the tank in 5 hours, while an inlet pipe can fill the same tank at the rate of 6 litres per minute. When the tank is full, the inlet is opened and the tank gets empty in 8 hours due to the leakage. Find the capacity of the tank.

A

1800 litres✓✗

B

3600 litres✓✗

C

4800 litres✓✗

D

5760 litres✓✗

Explanation

The leak alone empties the tank in 5 hours, so it drains C5 per hour, where C is the capacity. With the inlet open the tank empties in 8 hours, so the net loss = C8 per hour.
Inlet rate = 6 litres per minute = 360 litres per hour.
C5 - C8 = 360, so 3C40 = 360 and C = 4800 litres.

Question 13

Pipes A and B fill a tank in 5 and 6 hours respectively. Pipe C empties the tank in 12 hours, if you open all the three pipes together this tank will be filled in?

A

3 917 hours✓✗

B

4.5 hours✓✗

C

1.25 hours✓✗

D

4 717 hours✓✗

Explanation

Pipes A and B fill 15 and 16 of the tank per hour and pipe C empties 112.
Net rate = 15 + 16 - 112 = 12 + 10 - 560 = 1760.
Time = 6017 = 3917 hours.

Question 14

Two pipes A and B can fill a tank in 12 and 24 minutes respectively. If both the pipes are used together, how long will it take to fill the tank?

A

9 min✓✗

B

8 min✓✗

C

4 min✓✗

D

6 min✓✗

Explanation

Pipe A fills 112 and pipe B fills 124 of the tank per minute.
Together = 112 + 124 = 324 = 18.
They fill the tank in 8 minutes.

Question 15

Two pipes A and B can fill a cistern in 37.5 minutes and 45 minutes respectively. This cistern will be filled in half an hour if both the pipes are opened together initially and pipe B is then turned off after X minutes. What is X?

A

10 minutes✓✗

B

15 minutes✓✗

C

12 minutes✓✗

D

9 minutes✓✗

Explanation

Both pipes fill the cistern in half an hour, but B is closed after X minutes, so A works for 30 minutes and B works for X minutes.
A alone in 30 minutes fills 3037.5 = 45 of the cistern. The remaining 15 is filled by B.
X = 15 × 45 = 9 minutes.

Question 16

A tank can hold 180 liters of water. A man opens a pipe, which starts filling the tank at 10 liters per minute. The man returns when the tank should have been full, but observes that due to a leak, it is still ¼ empty. How long will the leak take to drain the tank if it is full of water?

A

48 min.✓✗

B

72 min.✓✗

C

60 min.✓✗

D

36 min.✓✗

Explanation

At 10 litres per minute the tank should fill in 18010 = 18 minutes.
After 18 minutes it is 14 empty, so it holds 34 × 180 = 135 litres, and the leak has drained 180 - 135 = 45 litres in 18 minutes, that is 2.5 litres per minute.
The leak empties a full tank in 1802.5 = 72 minutes.

Question 17

2 pipes, A & B are connected to a tank ¾ full of water. If only A is opened, the tank will be filled in 4 minutes. If only B is opened, it will be drained in 18 minutes. If the tank is empty and both pipes are opened at the same time, how long will it take the tank to be filled?

A

48 min.✓✗

B

36 min.✓✗

C

60 min.✓✗

D

72 min.✓✗

Explanation

Pipe A fills the remaining 14 of the tank in 4 minutes, so A alone fills the whole tank in 16 minutes. Pipe B drains the 34 tank in 18 minutes, so B alone drains the whole tank in 24 minutes.
With both open, the net rate = 116 - 124 = 3 - 248 = 148.
An empty tank takes 48 minutes to fill.

Question 18

2 pipes can fill a cistern in 63 & 84 minutes. If both pipes are opened simultaneously, how long will it take?

A

24✓✗

B

12✓✗

C

26✓✗

D

36✓✗

Explanation

The pipes fill 163 and 184 of the cistern per minute.
Together = 4 + 3252 = 7252 = 136.
They take 36 minutes.

Question 19

3 pipes can fill a cistern in 15, 120 & 20 minutes. If all 3 are opened together, how long will it take?

A

8 min.✓✗

B

10 min.✓✗

C

12 min.✓✗

D

9 min.✓✗

Explanation

The pipes fill 115, 1120 and 120 of the cistern per minute.
Together = 8 + 1 + 6120 = 15120 = 18.
They take 8 minutes.

Question 20

A sink is 14 full when both the faucet & drain are opened. The faucet alone can fill the sink in 6 minutes while the drain alone can empty it in 8 minutes. How long will it take to fill the remaining 34 of the sink?

A

6 min✓✗

B

10 12 min✓✗

C

14 min✓✗

D

18 min✓✗

Explanation

The faucet fills 16 of the sink per minute and the drain empties 18 per minute.
Net rate with both open = 16 - 18 = 124 of the sink per minute.
Time to fill the remaining 34 = 34 ÷ 124 = 18 minutes.

Question 21

One tap takes 15 min to fill a tank, another tap takes 12 min to fill it, and a third tap can empty it in 20 min. If all three are opened together, in how much time would the tank be full?

A

100 min✓✗

B

5 min✓✗

C

11 min✓✗

D

10 min✓✗

Explanation

Combined rate = 115+112-120 = 110, giving a fill time of 10 minutes.

Question 22

A sink is 14 full when both the faucet and drain are opened. The faucet alone can fill the sink in 6 minutes while the drain alone can empty it in 8 minutes. How long will it take to fill the remaining 34 of the sink?

A

6 min.✓✗

B

10 12 min✓✗

C

14 min✓✗

D

18 min✓✗

Explanation

Net fill rate with both open = 16-18=124 per minute. Filling the remaining 34 takes (34)/(124)=18 minutes.

Question 23

Two pipes A and B can fill a tank in 6 hours and 4 hours respectively. They are opened for alternate hours starting with pipe A. How long will it take to fill the tank?

A

4 hrs✓✗

B

5 hrs✓✗

C

5.5 hrs✓✗

D

6 hrs✓✗

Explanation

Hour1(A):1/6. Hour2(B):+14=5/12. Hour3(A):+16=7/12. Hour4(B):+14=5/6. Hour5(A):+16=1 (full). Total=5 hours.

Question 24

Two taps A and B can fill a tank in 10 hours and 20 hours respectively. Due to a leakage, it actually takes 25 hours to fill the tank with both taps open. If the tank is full, how long would it take for the leakage alone to empty the whole tank?

A

1009 hours✓✗

B

10011 hours✓✗

C

507 hours✓✗

D

1007 hours✓✗

Explanation

Combined fill rate of A and B = 110 + 120 = 320 per hour. With the leak, the actual combined rate = 125 per hour. Leak (emptying) rate = 320 - 125 = 15 - 4100 = 11100 per hour. Time for the leak alone to empty a full tank = 10011 hours.

Question 25

Two pipes fill a cistern in 15 hrs and 20 hrs respectively. The pipes are opened simultaneously and it is observed that it took 26 min more to fill the cistern because of leakage at the bottom. If the cistern is full, then in what time will the leak empty it?

A

35 hrs✓✗

B

70 hrs✓✗

C

180 hrs✓✗

D

300 hrs✓✗

Explanation

Combined rate of the two pipes = 115 + 120 = 760, so time without leakage = 607 ≈ 8 hrs 34 min. With the leak, this becomes 9 hrs. So the combined (pipes + leak) rate is 19, and the leak's own rate = 760 – 19 = 1180. The leak alone empties the cistern in 180 hours.