TWO pipes X and Y can fill a cistern in 24 minutes and 32 minutes respectively. If both the pipes are opened together, then after how much time (in minutes) should Y be closed so that the tank is full in 18 minutes?

Correct Answer: 8 m

1/24+1/32 = 4+3/96

If tank is fill in 18 minutes so pipe ‘x’ will work for these 18 minutes

Pipe ‘x’ fills in 18 minuts =18×4=72 units

Remaining capacity = 96−72=24 units

So remaining capacity of tank/ cistern must be filled by pipe’y’

pipe y fills in 243=8 mins

So, after 8 minutes it must have been closed