A pump can fill a tank with water in 6 hours. Because of a leak, it took 12 hours to fill the tank. The leak can drain all the water in ?
Choices:
A) 12 hr  B) 11 hr  C) 13 hr  D) 14 hr  E) 16 hr

Rationale: work done by the leak in 1 hour = 1 / 6 - 1 / 12 = 1 / 12 leak will empty the tank in 12 hours answer is a
Answer: A