Question
A tank can be filled by Pipe A in 24 minutes and by Pipe
B in 30 minutes. Both pipes are opened together and after some time Pipe B is closed. If the tank is completely filled in 20 minutes, after how many minutes from the start was Pipe B closed?Solution
Let Pipe B be open for x minutes. Pipe A is open for the whole 20 minutes. Work done by A = 20/24 Work done by B = x/30 Total work = 1: 20/24 + x/30 = 1 5/6 + x/30 = 1 x/30 = 1/6 x = 5 minutes Pipe B was closed after 5 minutes.
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