Two pipes A and B can fill a tank in 15 minutes and 20 minutes respectively Both the pipes are opene...........

Quant (SSC) Pipes&cistern

Two pipes A and B can fill a tank in 15 minutes and 20 minutes respectively. Both the pipes are opened together but after 4 minutes, pipe A is turned off. What is the total time required to fill the tank?

10 min. 20 sec

11 min. 45 sec.

12 min. 30 sec.

14 min. 40 sec.

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Explanation:

Part filled in 4 minutes =4(1/15+1/20) = 7/15
Remaining part =(1-7/15) = 8/15
Part filled by B in 1 minute =1/20 : 8/15 :: 1:x
x = (8/15*1*20) = 10 2/3min = 10min 40sec
The tank will be full in (4 min. + 10 min. + 40 sec.)
= 14 min. 40 sec