Pipes&cistern

Quantitative Aptitude (CGL)

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45:30

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Two pipes P and Q can fill a tank in 45 min. and 36 min. respectively. A water pipe can empty the tank in 30 min. First P and Q are opened. After 7 minutes, R is also opened. In how much time, the tank in full ?

46 min

52 min

56 min

60 min

Explanation:

Part filled in 7 min = 7(1/36 + 1/45) = 7/20.
Remaining part = (1 - 7/20) = 13/20.
Net part filled in 1 min. when P, Q and R are opened = (1/36 + 1/45 - 1/30) = 1/60.
Now, 1/60 part is filled in 1 min.
13/60 part is filled in (60*13/20) = 39 min.
Total time taken to fill the tank =(39 + 7) min. = 46 min.

By: Deepak Dawra

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