Bhanu Chaudhary
Poll
Professional
Asked: 2022-03-04T11:04:01+05:30

Pipe A which can fill a tank in 20 minutes is kept open for 5 minutes when the tank is empty. Then Pipe B which can fill the tank in 30 minutes is also opened. How long after Pipe A is opened will the tank be full?

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Pipe A which can fill a tank in 20 minutes is kept open for 5 minutes when the tank is empty. Then Pipe B which can fill the tank in 30 minutes is also opened. How long after Pipe A is opened will the tank be full?

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    1 Answer

    1. Professional

      Correct Answer: 14 minutes

      Pipe A fills 1/20th of the tank every minute. ln 5 minutes, it will fill 5×1/20=1/4th of the tank.

      After 5 minutes, Pipe B is also opened.

      Together, Pipe A and Pipe B fill 1/20+1/30=3+2/60=1/12th of the tank every minute.

      Together the pipes will fill an empty tank in 12 minutes.

      As Pipe A alone had filled 1/4th of the tank by the time Pipe B was opened, only 3/4ths of the tank needs to be filled when the 2 pipes are working together.

      To fill 3/4ths the tank, the two pipes will take 3/4×12=9 min.

      And, the total time taken = 5 + 9 = 14 minutes.

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