Q7 of 94 Page 45

A tap can fill a tank in 15 minutes. Another tap can empty it in 20 minutes. Initially the tank is empty. If both the taps start functioning, when will the tank become full?

Time taken by A = 15 min

Work done by A in 1 min =


Time taken by B = 30 min


Work done by B in 1 min =


Work done by all three A, B in 1 min = - =


(∵ B empties the tank we use negative there)


Time taken to fill to the tank is 60 min


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