An electric pump can fill a tank in 5 hours. Because of a leak in the tank, it took 10hours to fill the tank. If the tank is full, how much time will the leak take to empty it? Choose one:  A) 10 hours  B) 12 hours  C) 8 hours  D) 5 hours  E) 15 hours

Rationale: "work done by the leak in 1 hour = 1 / 5 - 1 / 10 = 1 / 10 the leak will empty the tank in 10 hours answer is a"
Answer: A