Two pipes A and B can fill a tank in 10 minutes and 20 minutes respectively Both the pipes are opene...........

Quant (SSC) Pipes&cistern

Two pipes A and B can fill a tank in 10 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 ?

12m

10m

16m

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Explanation:

A + B in 4 minute = 4 ( 1 / 10 + 1 / 20 )
= 4(2+1/20) = 12/20 = 3/5
Part remaning = 1 – ( 3 / 5 ) = 2 / 5
1 / 20 part is filled by B in 1 minute
2 / 5 part will be filled in = ( 20)* ( 2 / 5 ) = 8 minutes
Total = 8+4 = 12m
Hence, option 1 is the correct answer.