Two pipes P and Q can fill a cistern in 12 minutes and 16 minutes respectively. Simultaneously both the pipes are opened together, then after how much time Q should be closed so that the tank is full in 9 min?
Q1. Two pipes P and Q can fill a cistern in 12 minutes and 16 minutes respectively. Simultaneously both the pipes are opened together, then after how much time Q should be closed so that the tank is full in 9 min?
Answer: 4 min
Explanation: P works for 9 min, Q for t min: 9/12 + t/16 = 1 → t/16 = 1/4 → t = 4 minutes.