Pipes A and B can fill a tank in one hour and two hours respectively while pipe C can empty the filled up tank in one hour and fifteen minutes. A and C are turned on together at 9 a.m. After 2 hours. Only A is closed and B is turned on. When will the tank be emptied?

Answer: Option D

Solution

Answer: Option D

Solution:

At 11 am, A is closed, now (B + C) will work together
B + C = 5 - 8 = -3
The time was taken to fill 4 unit
$$t=\frac{4}{3}=1\frac{1}{3}=1\text{hr}20\min$$