This Article consist of most important ” Pipes and Cistern Problems ” topic that are mostly asked in all competitive exams. We collected these questions from the students who appeared in exams. Now try to solve these questions.
Pipes and Cistern Problems
Question : 1 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
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Correct Answer : D
Explanation :
Net part filled in 1 hours = (1/4 -1/9)= 5/36.
The cistern will be filled in 36/5 hrs i.e., 7.2 hrs
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Question : 2 Two Pipes A and B can fill a tank in 6 hours and 4 hours respectively.If they are opened on alternate hours and if pipe A is opened first,in how many hours, the tank shall be full?
A. 4
B. 4.5
C. 5
D. 5.5
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Correct Answer : C
Explanation :
A’s work in 1 hour=1/6 , B’s work in 1 hour=1/4
(A + B)’s 2 hour’s work when opened alternatively=(1/6+1/4)=5/12.
(A + B)’s 2 hour’s work when opened alternatively=10/12=5/6
Now,it is A’s turn and 1/6 part is filled by A in 1 hour.
So, total time taken to fill the tank=(4+1) hrs=5 hrs
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Question : 3 Two pipes can fill a tank in 20 and 24 minutes respectively and a waste pipe can empty 3 gallons per minute. All the three pipes working together can fill the tank in 15 minutes. The capacity of the tank is:
A. 60 gallons
B. 100 gallons
C. 120 gallons
D. 180 gallons
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Correct Answer : C
Explanation :
Work done by the waste pipe in 1 minute
= 1/15 – (1/20 + 1/24)
= (1/15 – 11/120)
= -1/40. [-ve sign means emptying]
Volume of 1/40 part = 3 gallons.
Volume of whole = (3 x 40) gallons = 120 gallons.
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Question : 4 Two pipes A and B can fill a cistern in (75/2) minutes and 45 minutes respectively. Both pipes are opened. The cistern will be filled in just half an hour, if the B is turned off after:
A. 5 min
B. 9 min
C. 10 min
D. 15 min
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Correct Answer : B
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/225 + (60 -2x)/75 = 1
11x + 180 – 6x = 225.
x = 9.
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Question : 5 A pump can fill a tank with water in 2 hours. Because of a leak, it took 7/3 hours to fill the tank. The leak can drain all the water of the tank in:
A. 13/3
B. 7
C. 8
D. 14
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Correct Answer : D
Explanation :
Work done by the leak in 1 hour = (1/2) – (3/7)
= 1/14
Leak will empty the tank in 14 hrs
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