A water tank is two-fifths full. Pipe A can fill the tank in 10 minutes, and pipe B can empty it in 6 minutes. If both pipes are open, how long will it take to empty or fill the tank completely?
A
6 minutes to empty
B
7 minutes to fill
C
6 minutes to fill
D
7 minutes to empty
Correct Option:
A
Explanation
The tank initially contains 2/5 of its capacity. Pipe A fills at 1/10 tank per minute, and pipe B empties at 1/6 tank per minute. The net rate is 1/10 - 1/6 = -1/15 tank per minute, so the tank is emptying. Time required = (2/5)/(1/15) = 6 minutes.
