Sunday, August 17, 2014

time and work

A tank can be filled by one tap in 20 mins and by another tap in 25 mins.Both the taps are kept open for 5 mins and then the second tap is turned off. In how many minutes more is the tank completely filled?


Answer:
first tap fills 1/20 th of the tank in a min.
second tap fills 1/25 of the tank in a min
they together fill (1/20 + 1/25) of the tank in a min,
Therefore in 5 mins, 5 x (1/20 + 1/25) = 9/20 th of the tank is filled
tank remaining empty after 5 mins = 11/20
time taken by first tap to fill the tank = (11/20) / (1/20) = 11 mins

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