An electric pump can fill a tank in 3 hours. Because of a leak in the tank, it takes 3 hours 30 minutes to fill the tank. How much time will the leak take to drain all the water from the tank and empty it?
A
10 hours
B
13 hours
C
17 hours
D
21 hours
Correct Option:
D
Explanation
Pump rate = 1/3 tank/hour. With the leak, the tank fills in 3.5 hours, so the net rate = 2/7. Leak rate = 1/3 − 2/7 = 1/21. Thus, the leak alone empties a full tank in 21 hours.
