Pipes and Cisterns

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_________?

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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

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?

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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

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.

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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
Work done by leak in 1 hour = (1/8 – 1/10) = 1/40
The leak will empty the cistern in 40 hours.

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?

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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
Explanation:
Net filling in 1 hour = (1/2 – 1/3) = 1/6
Time taken to fill the cistern = 6 hours

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

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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
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

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?

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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
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.

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?

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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
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

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?

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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
Explanation:
Work done by the waste pipe in 1 minute = 1/15 – (1/20 + 1/24) = – 1/40
Volume of 1/40 part = 3 gallons
Volume of whole = 3 * 40 = 120 gallons.