Pipes and Cistern - Quantitative Aptitude (MCQ) questions

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 ?
- Published on 20 Apr 16

a. 860 litre
b. 980 litre
c. 1120 litre
d. 1400 litre
e. None of these
Answer  Explanation 

ANSWER: 1400 litre

Explanation:
Let the time taken by the 1st pipe to fill the tank be x hours.
When both the pipes are open, it is given that:
1/x + 1/6 = 1/(4.2) of tank is filled in 1 hour.
1/x + 1/6 = 5/21
21(6 + x) = 30 x
9x = 126
x = 14 hours
Therefore, capacity of the tank = 100 * 14 = 1400 litres.


2)   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?
- Published on 06 Apr 16

a. 2 hours
b. 2.4 hours
c. 3 hours
d. 3.5 hours
Answer  Explanation 

ANSWER: 2.4 hours

Explanation:
Part filled by (P + Q + R) in 1 hour = (1/4 + 1/8 + 1/24) = 10/24
All the three pipes together will fill the tank = 24/10 = 2.4 hours


3)   Two pipes P and Q can fill a tank in 10 hours and 14 hours respectively. If both pipes are opened simultaneously, how much time will be taken to fill the tank?
- Published on 28 Mar 16

a. 4 hours 20 min
b. 5 hours 49 min
c. 3 hours 50 min
d. 3 hours 22 min
Answer  Explanation 

ANSWER: 5 hours 49 min

Explanation:
Part filled by P in 1 hour = 1/10
Part filled by Q in 1 hour = 1/14
Part filled by (P + Q) in 1 hour = ( 1/10 + 1/14) = (6/35)
Time taken to fill the tank is (35/6) = 5 hours 49 min


4)   A inlet pipe can fill a tank in 12 hours and an outlet pipe can empty the tank in 16 hours. If both the pipes are opened simultaneously, find the time taken to fill the tank.
- Published on 06 Jul 15

a. 36 hours
b. 12 hours
c. 4 hours
d. 48 hours
Answer  Explanation 

ANSWER: 48 hours

Explanation:
As the inlet can fill the tank in 12 hours, in one hour it will fill 1/12th of the tank.
Similarly, the outlet pipe in one hour can empty 1/16th part of the tank.
If both are opened simultaneously, the part of the tank filled in one hour is:
1/12 - 1/16 = 1/48
Hence, the tank gets filled in 48 hours.


5)   If pipe A can fill the tank in 45 minutes and pipe B in 30 minutes, find the time to fill the tank if both the pipes are opened together.
- Published on 06 Jul 15

a. 12 minutes
b. 20 minutes
c. 18 minutes
d. 15 minutes
Answer  Explanation 

ANSWER: 18 minutes

Explanation:
In 1 minute pipe A can fill 1/45th part of the tank and pipe B can fill 1/30th part of the tank. If they are opened simultaneously then in 1 minute they can fill (1/45

+ 1/30) part of the tank = 1/18th part of the tank.
Hence, in 18 minutes the tank gets filled if pipes A & B are opened together.


6)   If a pipe can fill a tank in 6 hours, find the part of tank it fills in one hour.
- Published on 06 Jul 15

a. 1/6
b. 2/3
c. 1/2
d. None of these
Answer  Explanation 

ANSWER: 1/6

Explanation:
Let the capacity of the tank be C litres.
Time to fill the tank = 6 hours
Hence, in 1 hour C/6 litres gets filled.
Therefore, 1/6th part of the tank gets filled in one hour.


7)   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.
- Published on 06 Jul 15

a. 1800 litres
b. 3600 litres
c. 4800 litres
d. 5760 litres
Answer  Explanation 

ANSWER: 4800 litres

Explanation:
The capacity of the tank is given by C = (p*q*r)/(r – p) litres
Where, p = time in which the leakage can empty the tank in hours = 5 hours
q = rate at which the inlet fills the tank in lph = 6*60 = 360 lph
r = time in which the tank gets emptied in hours = 8 hours
Hence, C = (5*360*8)/(8 – 5)
C = 4800 litres


8)   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?
- Published on 15 Jun 15

a. 3 9/17 hours
b. 4.5 hours
c. 1.25 hours
d. 4 7/17 hours
Answer  Explanation 

ANSWER: 3 9/17 hours

Explanation:
It is given that Pipe A,B and C work simultaneously.

Pipe A and B are filling the tank and Pipe C is emptying it.

In 1 hour volume of tank filled by Pipe A: 1/5th

In 1 hour volume of tank filled by Pipe B: 1/6th

In 1 hour volume of tank emptied by Pipe C: 1/12th

Working together Pipe A B and C fill x volume of tank.

=>1/x = (1/5)+(1/6)-(1/12)

=>x=60/17 hours


9)   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?
- Published on 15 Jun 15

a. 9 min
b. 8 min
c. 4 min
d. 6 min
Answer  Explanation 

ANSWER: 8 min

Explanation:
Tank can be filled by pipe A in 12 minutes and pipe B in 24minutes.

=> Part filled by A in 1 minute= 1/12

=> Part filled by B in 1 minute= 1/24

=> Part filled by both in 1 minute= 1/12 + 1/24

= 3/24=1/8

Time taken to fill the entire tank = 8 minutes


10)   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?
- Published on 12 Jun 15

a. 10 minutes
b. 15 minutes
c. 12 minutes
d. 9 minutes
Answer  Explanation 

ANSWER: 9 minutes

Explanation:
Let B be turned off after X minutes.

Part of water will be filled by A + B in x minutes + After tap B is closed rest filled by A in (30-x) minutes = 1

=> x/(time taken to fill the container by each separately) + 30 - x/(time taken to fill the container by A alone) = 1
=> x(2/75 + 1/45) + (30-x)2/75 = 1
=> 11x + 180 – 6x = 225

Therefore, x = 9 minutes


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