Question

the inlet of the pipe of a tank fills it in 4 hours, while the other pipe empties it in 8 hours. find the time taken to fill the tank if both the pipes are opened together

Answer 1

Pipe can fill tank in 1 hour=1/4.
Pipe can empty tank in 1 hour=1/8.
Therefore,
Both pipes can fill tank in=1/4-1/8
=1/8.
1÷1/8=8hours.