A and B are pipes such that A can empty the tank in 60 minutes and B can fill in 30 minutes The tank...........

Quantitative Aptitude ( CCS) Pipes&cistern

A and B are pipes such that A can empty the tank in 60 minutes and B can fill in 30 minutes. The tank is full of water and pipe A is opened. If after 18 minutes, pipe B is also opened, then in how much total time the tank will be full again?

32 minutes

29 minutes

36 minutes

23 minutes

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Explanation:

Answer & Explanation
36 minutes
Explanation:
Emptying pipe A is opened first for 18 minutes, so in 18 minutes the part of tank it has emptied is (1/60)*18 = 9/30
Now filling pipe is also opened, now since only 9/30 of the tank is empty so 9/30 is only to be filled by both pipes, let it take now x minutes, so
(1/30 – 1/60)*x = 9/30
Solve, x= 18
So total = 18+18 = 36 minutes [total time is asked – 18 minutes when emptyimh pipe was only opened, 18 minutes when both were operating.]