Pipe & Cisterns

Fast trick to solve the pipe and cisterns.

Two pipe 'A' and 'B' can fill a tank in 4 hr and 6 hr respectively.if both the pipe are opened simultaneously.How much time be taken to fill the tank?

STEP 1 :

Pipe 'A' can fill the tank in 4 hr
then in 1 hr. = 1 / 4 part of tank

Pipe 'B' can fill the tank in 6 hr
then in 1 hr. = 1 / 6 part of tank

STEP 2 :

Both pipe fill in 1 hr = 1 / 4 + 1 / 6 part of tank

in 1 hr.= 3 + 2 / 12 part of tank

in 1 hr.= 5 / 12 part of tank

1 * 12/5= 1 part of tank

12/5 hr = 1 part of tank

Tank will be filled in 12/5 hr.