Question

A large tanker can be filled by two pipes a and b in 60 minutes and 40 minutes respectively. how many minutes will it take to fill the tanker from empty state if b is used half the time and a and b fill it together for the oyher half

Answer 1

Assume the tanker to be of 2400ml capacity for an easy solution (60x40=2400),

Pipe A can fill it in 60 minutes
So, the speed of pipe A is 40 ml/min

Pipe B can fill it in 40 minutes
So, the speed of pipe B is 60 ml/min

if b is used half the time
So water in tanker will be
= ( X/2 ) min x 60 ml/min
= X x 30 ml

if a and b are used other half the time
So water in tanker will be
= ( X/2 ) min x ( 40 ml/min + 60 ml/min )
= ( X/2 ) min x 100 ml/min
= X x 50 ml

So, now that the tanker is filled that means
2400ml = X x 30 ml + X x 50 ml
2400 = X x 80
X = 30

So, 30 minutes will it take to fill the tanker from empty state if b is used half the time and a and b fill it together for the other half.