Pipe A is capable of filling a tank in 16 minutes while Pipe B can fill the same tank in 24 minutes. Both pipes are opened together, but after 4 minutes, the rate of Pipe A doubles and the rate of Pipe B becomes half of its original, How many more minutes will it take to fill the tank completely?
Show answer & explanation
Correct answer: A
Explanation
The correct answer is option 1 i.e. 4 min.
Pipe A's original rate = 1/16
Pipe B's original rate = 1/24
Work in 4 minutes together = 4(1/16 + 1/24) = 4 × 5/48 = 5/12
Remaining part = 1 – 5/12 = 7/12
After 4 min:
New A rate = 2 × 1/16 = 1/8
New B rate = 1/2 × 1/24 = 1/48
New combined rate = 1/8 + 1/48 = 7/48
Time to fill remaining part = (7/12) ÷ (7/48) = (7/12) × (48/7) = 4 minutes