A pump can fill a tank with a water in 2 hours. Because of a leak, it took 4 hours to fill the tank. The leak can drain all the water of the full tank in how many hours? Choose the correct choice from the following answers
A) 2  B) 3  C) 4  D) 5  E) 6
The rate of the pump + leak = 1/4   1/2 - leak's rate = 1/4   leak's rate = 1/2 - 1/4 = 1/4   The leak will empty the tank in 4 hours.   The answer is 4.
<result>C</result>
A pump can fill a tank with a water in 2 hours. Because of a leak, it took 4 hours to fill the tank. The leak can drain all the water of the full tank in how many hours?