# Pipes and Cistern MCQs for Competitive Examination

## Solve the following problems.

**Q. 21**

A pipe can fill a cistern in 9 hours. Due to a leak in its bottom, the cistern fills up in 10 hours. If the cistern is full, then in how much time will it be emptied by the leak?

(A) 70 hours

(B) 80 hours

(C) 90 hours

(D) 100 hours

**Answer**: (C) 90 hours **Explanation**: N/A

**Q. 22**

Three pipes A, B and C can fill a tank in 6 hours. After working together for 2 hours, the pipe C is closed and A and B can fill the remaining part in 7 hours. The number of hours taken by C alone to fill the tank is

(A) 10

(B) 12

(C) 14

(D) 16

**Answer**: (C) 14 **Explanation**: N/A

**Q. 23**

Two pipes A and B can fill a tank with water in 30 minutes and 45 minutes respectively. The water pipe C can empty the tank in 36 minutes. First A and B are opened. After 12 minutes C is opened. The total time (in minutes) in which the tank will be oiled up is

(A) 30

(B) 12

(C) 36

(D) 24

**Answer**: (D) 24**Explanation**: N/A

**Q. 24**

A cistern has two pipes. One can fill it with water in 8 hours and others can empty it in 5 hours. In how many hours will the cistern be emptied if both the pipes are opened together when (3/4) of the cistern is

already full of water

(A) 13(1/3) hours

(B) 10 hours

(C) 6 hours

(D) 3(1/3) hours

**Answer**: (B) 10 hours**Explanation**: N/A

**Q. 25**

Three pipes A, B and C can fill a tank in 6 hours, 9 hours and 12 hours respectively. B and C are opened for half an hour, then A is also opened. The time taken by the three pipes together to fill the remaining part of the tank is

(A) 3 hours

(B) 2 hours

(C) 2(1/2) hours

(D) 3(1/2) hours

**Answer**: (C) 2(1/2) hours**Explanation**: N/A

**Q. 26**

12 pumps working 6 hours a day can empty a completely filled reservoir in 15 days. How many such pumps working 9 hours a day will empty the same reservoir in 12 days?

(A) 15

(B) 9

(C) 10

(D) 12

**Answer**: (C) 10**Explanation**: N/A

**Q. 27**

A pipe can fill a tank in x hours and another pipe can empty it in y (y > x) hours. If both the pipes are open, in how many hours will the tank be filled?

(A) (x – y) hours

(B) (y – x) hours

(C) xy/(x – y) hours

(D) xy/(y – x) hours

**Answer**: (D) xy/(y – x) hours**Explanation**: N/A

**Q. 28**

A pipe can empty a tank in 40 minutes. A second pipe with a diameter twice as much as that of the first is also attached with the tank to empty it. The two together can empty the tank in

(A) 8 minutes

(B) 13(1/2) minutes

(C) 30 minutes

(D) 38 minutes

**Answer**: (A) 8 minutes**Explanation**: N/A

**Q. 29**

A pipe of diameter d can drain a certain water tank in 40 minutes.The time taken by a pipe of diameter 2d for doing the same job in

(A) 5 minutes

(B) 10 minutes

(C) 20 minutes

(D) 80 minutes

**Answer**: (B) 10 minutes**Explanation**: N/A

**Q. 30**

Three pipes P, Q and R can separately fill a cistern in 4, 8 and 12 hours respectively. Another pipe S can empty the completely filled cistern in 10 hours. Which of the following arrangements will fill the empty cistern in less time than others?

(A) Q alone is open

(B) P and S are open

(C) P, R and S are open

(D) P, Q and S are open

**Answer**: (D) P, Q and S are open**Explanation**: N/A

**Q. 31**

A swimming pool has 3 drain pipes. The first two pipes A and B, operating simultaneously, can empty the pool in half the time that of C, the 3 rd pipe, alone takes to empty it. Pipe A working alone takes half the time taken by pipe B. Together they take 6 hours 40 minutes to empty the pool. Time taken by pipe A to empty the pool is

(A) 10 hours

(B) 15 hours

(C) 30 hours

(D) 7 hours

**Answer**: (B) 15 hours**Explanation**: Time taken by pipe B = 2x hours(suppose)

hence, Time taken by pipe A = x hours

Time taken by pipe C = 1/((1/2x) + (1/x)) = 4x/3

According to the question, (1/x) + (1/2x) + (3/2x) = 1/(6 hour 40 minutes) = 3/20

Therefore, x = 15 hours

**Q. 32**

A tank can be filled by pipe A in 2 hours and pipe B in 6 hours. At 10 a.m. pipe A was opened. At what time will the tank be filled if pipe B is opened at 11 a.m.?

(A) 12.45 a.m

(B) 5 p.m

(C) 11.45 a.m

(D) 12 p.m

**Answer**: (C) 11.45 a.m**Explanation: **N/A

**Q. 33**

A water tap fills a tub in p hours and a sink at the bottom empties it in q hours. If p < q and both tap and sink are open, the tank is filled in r hours; then

(A) (1/r) = (1/p) + (1/q)

(B) (1/r) = (1/p) – (1/q)

(C) r = p + q

(D) r = p – q

**Answer**: (B) (1/r) = (1/p) – (1/q)**Explanation**: N/A

**Q. 34**

A tap drips at a rate of one drop/sec. 600 drops make 100 ml. The number of litres wasted in 300 days is

(A) 4320000

(B) 432000

(C) 43200

(D) 4320

**Answer**: (A) 4320000**Explanation**: N/A

**Q. 35**

A leak in the bottom of a tank can empty the full tank in 6 hours. An inlet pipe fills water at the rate of 4 litres a minute. When the tank is full, the inlet is opened and due to the leak, the tank is empty in 8 hours. Find the capacity of the tank?

(A) 5760 litres

(B) 96 litres

(C) 10 litres

(D) 24 litres

**Answer**: (A) 5760 litres**Explanation**: Work done in 1 hour = (1/6) – (1/8) = 1/24

Work done in 1 minute = (1/24) * (1/60) = 1/1440

According to the question volume of 1/1440 part = 4 litre

Volume of whole tank = 1440 * 4 = 5760 litre

**Q. 36**

Two taps A and B can fill a tank in 10 hours and 12 hours respectively. If the two taps are opened at 10 a.m., then at what time (in p.m.) should the tap A be closed to completely fill the tank at exactly 4 p.m.?

(A) 2

(B) 3

(C) 1

(D) 1.30

**Answer**: (B) 3**Explanation**: N/A

**Q. 37**

Two inlet pipes can fill a cistern in 10 and 12 hours respectively and an outlet pipe can empty 80 gallons of water per hour. All the three pipes working together can fill the empty cistern in 20 hours. What is the capacity (in gallons) of the tank?

(A) 360

(B) 300

(C) 600

(D) 900

**Answer**: (C) 600**Explanation**: L. C. M of 10, 12 and 20 = 120

Let the capacity of the tank = 120x

In 1 hour, the first pipe fills = 12x, and the second pipe fills = 10x, the outlet pipe empties 80 gallons/hour

According to the question,

(12x + 10x – 80) * 20 = 120x

therefore x = 5

hence the capacity of the tank = 120x = 120 * 5 = 600 gallons

**Q. 38**

Pipe A can fill a tank in 6 hours. Pipe B can fill the same tank in 8 hours. Pipe A, B and C together can fill the same tank in 12 hours. Then which of the following statement is true for pipe C?

(A) It can fill the tank in 4 hours 40 minutes

(B) It can fill the tank in 4 hours 48 minutes

(C) It can empty the tank in 4 hours 48 minutes

(D) It can empty the tank in 4 hours 40 minutes

**Answer**: (C) It can empty the tank in 4 hours 48 minutes**Explanation**: Let pipe C can fill the tank in x hours

According to the question, (1/6) + (1/8) + (1/x) = (1/12)

hence x = -(24/5)

Hence pipe C can empty the tank in 4 hours 48 minutes

**Q. 39**

Two pipes A and B can fill an empty tank in 8 and 12 hours respectively. They are opened alternatively for 1 hour each, starting with pipe A first. In how many hours will the empty tank be filled?

(A) 9(1/3)

(B) 9

(C) 9(1/2)

(D) 9(1/4)

**Answer**: (C) 9(1/2)**Explanation**: N/A

**Q. 40**

Pipes A and B can fill a tank in 6 hours and 9 hours respectively and pipe C can empty the full tank in 12 hours. If all three pipes are opened together when a tank is empty, in how many hours will 35% of the tank be filled?

(A) 1.9

(B) 1.5

(C) 1.6

(D) 1.8

**Answer**: (D) 1.8**Explanation**: N/A