If two pipe 'A' and 'B' operate both at the same time that can fill a tank in 5 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) = 1/5
x + 5 + x / x(x + 5) = 1/5
2x + 5 / x2 + 5x= 1/5
10x + 25 = x2 + 5x
so equation will be:
x2-5x-25 = 0
x=8 or x= -3
so the result will be '8 hr' because time must be positive value.
Watch Youtube video of Pipe & Cisterns for better understanding.