Question

A cistern can be filled by pipes A and B in 4 hours and 6 hours respectively. When full, the tank can be emptied by a pipe C in 8 hours. If all the taps be turned on at the same time, the cistern will be full in

Answer 1

Part filled in 1 hr = (1/4 + 1/6) = 5/12, Part emptied in 1 hr = 1/8

Net filling in 1 hr = (5/12 - 1/8) = 7/24

therefore

Time taken to fill the tank = 24/7 hr

= 3 hours 26 minute