**Pipe and Cistern Questions With Solutions For SSC, Bank, Railway**

**Pipe and Cistern Concepts : **LCM denote the capacity of tank. A fill the tank in 10 hours and B empty the tank in 15 hours. LCM (capacity of tank) is 30 Litres. A fill the tank in 1 hour = 3 Litres and B fill the tank in 1 hour = 2 Litres.

**1.** Two pipes A and B fill a tank in 20 minutes and 30 minutes. If both pipes are open together, how much time tank will take to be completely full.

LCM of A and B = 60. After this, allegation them.

A do work in 1 mins = 3 units

B do work in 1 mins = 2 units

(A+B) ‘s efficiency = 3 + 2 = 5

Total time taken to full the tank = 60/5 = 12 minutes.

**2.** If a tank is 1/3rd part, 80 litres water come in tank. How many litres water will be in tank if it is only half filled?

**Ans.** 1/3 —— 80 litres

1/2 —— (80*****(1**/**2))**/**(1/3)

—— 40 * 3 = 120 litres

**3. **If three pipes A, B and C can fill the tank in 12, 15 and 20 hours respectively. If pipe A is remain open and B, C fill the tank 1 hour each in an alternate way, how much time tank will take to be full.

**Ans.**

LCM of A,B and C = 60, allegation them.

In First hour, (A+B) = 5+4 = 9 units

In Second hour, (A+C) = 5+3 = 8 units

In two hours, 9+8 = 17 units

51 units = (51/17) * 2 = 6 hours

Remaining units = 60 – 51 = 9 units (which will be filled by A and B in only 1 hour)

Total time taken to fill the tank = 6 + 1 = 7 hours

**4. **One tap can make empty the tank in 1 hour and second tap can also empty the tank in 30 minutes. If both taps are opened together, how much time will take it to be emptied?

Ans.

(A+B) can emptied the tank in 1 hour = (1+2) = 3 units

Total time taken to empty the tank = 60/3 = 20 mins

**5. **One pipe can full a tank in 5 hours. And second pipe can empty the tank in 4 hours. If the tank is completely full and both pipes are opened, how much time tank will take to empty the tank?

**Ans.**

A+B in 1 hours = 4-5 = -1 units

Total time taken to empty the tank = 20/1 = 20 hours.

**6.** Two taps A & B can fill a tank in 48 min and 36 min. If both taps are opened together, after how much time tap A is closed so that the whole tank fill in 25 min 30 sec.

Total work = LCM of A & B = 144 unit

A work in 1 minutes = 3 units

B work in 1 minutes = 4 units

B has to complete it in 25(1/2) min = 4 * (51/2) = 102 units

Remaining unit = 144 – 102 = 42 units

Tap A should be closed after = 42/3 = 14 mins.

**7. **Two taps can fill a tub in 5 minutes and 7 minutes respectively. A pipe can empty it in 3 minutes. If all three tapes are kept open simultaneously, when will the tub be full?

+21 –> A —> 5 min

+15 –> B —> 7 min

-35 –> C —> 3 min

________________

1 –> A +B + C

LCM of A, B and C = 105

Time taken by all three pipes to fill the tank = 105/1 = 105 minutes.

**8. **A pipe can fill a cistern in 12 minutes and another pipe can empty it in 15 minutes, but a third pipe can empty it in 6 minutes. The first two pipes are kept open for 5 minutes in the beginning and then third pipe is also opened. Number of minutes taken to empty the cistern is

+5 –> A —> 12 minutes

+4 –> B —> 15 minutes

-10 –> C —> 6 minutes

____________________

-1 –> A + B + C

9 * 5 = 45 Litres (filled- A and B opened for 5 minutes.)

Capacity of tank or LCM = 60 Litres

Time taken to empty the cistern = 45 minutes.

**9. **Two pipes A and B can fill a tank in 24 min and 32 min respectively. If both the pipes are opened simultaneously, after how much time B should be closed so that the tank is full in 18 minutes?

+4 –> A —-> 24 min

+3 –> B —> 32 min

—————————

+7 —-> A + B

LCM or capacity of tank = 96

Consider both open till x minutes.

7 * X min + 4 (18-x) = 96

solve, x = 8 minutes.

After 8 minutes, B will be closed.

**Logical Concept : **A will fill till 18 minutes when B is closed. = 4 * 18 = 72 Litres.

Remaining = 96 – 72 = 24

24/3 = 8 minutes.

**10. **A cistern can be filled by two supply pipes in 20 min and 30 min respectively. But a waste pipe can empty it in an hour. Both the supply pipes were opened together to fill the empty cistern, but by mistake the waste pipe was also open. How much later was the waste pipe closed, if the cistern is filled in 14 minutes?

+3 –> A –> 20

+2 –> B –> 30

-1 –> C –> 60

_______________

+4 –> A + B + C

LCM = 60

5 * 14 = 70

10/1 = 10 minutes

**11. **A leak in the bottom of a tank can empty it in 12 hours. A tap which can added 20 litre per minute is turn on. Both the taps are opened now, then the tank is emptied in 20 hours. Find the capacity of the tank?

-5 —> A —> 12 hour

-3 —> A + B —> 20 hour

____________________

2+ —> B (B is filling 2 litres in 1 hour)

B will take to fill = 60/2 = 30 hours

LCM = 60 min

1 min —- 20 Litres

1 hour — 20 * 60 * 30

Capacity of tank = 36000

12. A tank has a leak which would empty the completely filled tank in 10 hours. If the tank is full and a tap which admits 4 litres of water per minute in the tank, the leak takes 15 hours to empty the tank. What is the capacity of the tank?

**All the best for your upcoming exam!**

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