☼ Pipes ( may be inlet or may be outlet )  &  Cisterns ( or tank or reservoir )  :

 If  a pipe can fill a tank in  x  hrs. and another pipe can empty the full tank in  y   hrs

( where y > x ), then on opening both the pipes, the net part filled in 1 hr  =

 Time taken to empty the tank is  =    hrs.

Click here to see examples