A tank can be filled by a tap 20 min & by another 25 min. Both taps are kept open for 5 min & then second is turned off.

Question

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

Answer 1

Let the tank be 1000 liters. Discharge rate of first tap is 1000/20 or 50 liter per minute. Smilarly discharge of the second tap is 40 liter per minute. When both the taps are open for five minutes, a discharge of (50+40)*5 or 450 liter has taken place and we are left with 550 liters to be filled. This can be done in 550/50 or 11 minutes by the first tap alone. This problem can also be solved by assuming tank of Q liter capacity. In the answer Q will cancel in the numerator and denominator.