Pipe & Cisterns

Fast trick to solve the pipe and cisterns.

If two pipe 'A' and 'B' operate both at the same time that can fill a tank in 3 hr. A water pipe 'A' fill the tank '5 hr' faster than the pipe 'B' how many hr does it take the pipe 'A' to fill the tank.

STEP 1 :

Let the tank can be filled by pipe 'A' in x hr
than pipe 'B' in 'x + 5 hr'

so in 1hr tank filled by A = 1/x
and in 1hr tank filled by B = 1/(x + 5)


STEP 2 :

Now the equation will be:
1/x + 1/(x + 5) = 1/3

x + 5 + x / x(x + 5) = 1/3

2x + 5 / x2 + 5x= 1/3

6x + 15 = x2 + 5x

so equation will be:

x2-1x-15 = 0


x=4 or x= -3


so the result will be '4 hr' because time must be positive value.


Watch Youtube video of Pipe & Cisterns for better understanding.