Pipe & Cisterns

Fast trick to solve the pipe and cisterns.

Pipe 'A' can fill a tank in 3 hr while pipe 'B' empties the full tank in 10 hr.if both the pipes operate simultaneously, in how much time will the tank be filled?

STEP 1 :

Pipe 'A' can fill the tank in 3 hr
then in 1 hr. = 1 / 3 part of tank

Pipe 'B' can empty a tank in 10 hr
then in 1 hr. = 1 / 10 part of tank

STEP 2 :

Both pipe operate in 1 hr = 1 / 3 - 1 / 10 part of tank

in 1 hr.= 10 - 3 / 30 part of tank

in 1 hr.= 7 / 30 part of tank

1 * 30/7= 1 part of tank

30/7 hr = 1 part of tank

Tank will be filled in 30/7 hr.