Question

Two pipes a and b can fill a tank in 24 minutes and 32 minutes respectively. If both the pipes are opened simultaneously, after how much time should b be closed so that the tank is full in 18 minutes?

Answer 1

let t be time when tap b is closed.
then part of work done by both and a alone to complete in 18 days is
t(1/24 +1/32) + 1/24 =1/18
7t/96=1/18 - 1/24
t = 4/21
hence time to stop tap b is 21/4 = 5.25 minutes