Pipes & Cisterns Mcqs - Set 1

1)   Three taps A, B and C can fill a tank in 12, 15 and 20 hours respectively. If A is open all the time and B and C are open for one hour each alternately, the tank will be full in_________?

a. 6 hours
b. 6 2/3 hours
c. 7 hours
d. 7 1/2 hours
Answer  Explanation 

ANSWER: 7 hours

Explanation:
No explanation is available for this question!


2)   A cistern can be filled by a tap in 4 hours while it can be emptied by another tap in 9 hours. If both the taps are opened simultaneously, then after how much time will the cistern get filled?

a. 4.5 hrs
b. 5 hrs
c. 6.5 hrs
d. 7.2 hrs
Answer  Explanation 

ANSWER: 7.2 hrs

Explanation:
No explanation is available for this question!


3)   A tap can fill a tank in 6 hours. After half the tank is filled, three more similar taps are opened. What is the total time taken to fill the tank completely?

a. 3 hrs 15 min
b. 3 hrs 45 min
c. 4 hrs
d. 4 hrs 15 min
Answer  Explanation 

ANSWER: 3 hrs 45 min

Explanation:
No explanation is available for this question!


4)   A large tanker can be filled by two pipes A and B in 60 minutes and 40 minutes respectively. How many minutes will it take to fill the tanker from empty state if B is used for half the time and A and B fill it together for the other half?

a. 15 min
b. 20 min
c. 27.5 min
d. 30 min
Answer  Explanation 

ANSWER: 30 min

Explanation:
No explanation is available for this question!


5)   One pipe can fill a tank three times as fast as another pipe. If together the two pipes can fill the tank in 36 minutes, then the slower pipe alone will be able to fill the tank in:

a. 81 min.
b. 108 min.
c. 144 min.
d. 192 min.
Answer  Explanation 

ANSWER: 144 min.

Explanation:
No explanation is available for this question!


6)   A cistern is normally filled in 8 hours but takes two hours longer to fill because of a leak in its bottom. If the cistern is full the leak will empty it in.

a. 16 hrs
b. 20 hrs
c. 25 hrs
d. 40 hrs
Answer  Explanation 

ANSWER: 40 hrs

Explanation:
Work done by leak in 1 hour = (1/8 – 1/10) = 1/40

The leak will empty the cistern in 40 hours.


7)   One top can fill a cistern in 2 hours and another can empty the cistern in 3 hours. How long will they take to fill the cistern if both the taps are opened?

a. 5 Hours
b. 6 Hours
c. 7 Hours
d. 8 Hours
Answer  Explanation 

ANSWER: 6 Hours

Explanation:
Net filling in 1 hour = (1/2 – 1/3) = 1/6

Time taken to fill the cistern = 6 hours


8)   A top can fill a cistern in 8 hours and another can empty it in 16 hours. If both the taps are opened simultaneously the time (in hours) to fill the tank is

a. 8
b. 10
c. 16
d. 24
Answer  Explanation 

ANSWER: 16

Explanation:
Part filled by insert in 1 hour = 1/8

Part emptied by outlet in 1 hour = 1/16

Net filling in 1 hour = (1/8 – 1/16) = 1/16

Time taken to fill the tank = 1/16 hour= 16 hours


9)   Three pipes A, B and C can fill a tank in 6 hours. After working at it together for 2 hours. C is closed A and B can fill the remaining par 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  Explanation 

ANSWER: 14

Explanation:
Part filled in 2 hours = 2/6 = 1/3.

Remaining part = 1 – 1/3 = 2/3
(A + B)’s 1 hour work = 2/21
C’s 1 hour work = [(A + B + C)’s 1 hour work – (A + B)’s 1 hour work]
= (1/6 – 2/21) = 1/14
C alone can fill the tank in 14 hours.


10)   Two pipes A and B can fill a cistern in 37 1/2 minutes and 45 minutes respectively. Both pipes are opened. The cistern will be filled in just half an hour, if the pipe B is turned off after?

a. 5 min
b. 9 min
c. 10 min
d. 15 min
Answer  Explanation 

ANSWER: 9 min

Explanation:
Let B be turned off after x minutes. Then, part filled by (A + B) in x min + part filled by A in (30 – x) min = 1.

x(2/75 + 1/45) + (30- x) 2/75 = 1
11x + 180 – 6x = 225 => x = 9