Two pipes X and Y can fill a cistern in 24 min. and 32 min. respectively. If both the pipes are opened together, then after how much time Y should be closed so that the tank is full in 18 minutes?
Correct Answer: 8 min.
Explanation:
Let Y be closed after T min
Then, T x (1/ 24 + 1/32) + (18 - T) x 1/24 = 1
⇒ (7 x T)/96 + (18 - T)/24 = 1
or 7T + 72 - 4T = 96.
∴ 3T = 24
or T = 8 min.
