A pump can fill a tank with water in 2 hours. Because of a leak, it took 4 hours to fill the tank. The leak can drain all the water in ?  Choose the correct choice from the following choices.
A) 2hr	B) 1hr	C) 3hr	D) 4hr	E) 6hr
Work done by the leak in 1 hour = 1/2 - 1/4 = 1/4   Leak will empty the tank in 4 hours   Answer is 4hr
<result>D</result>
A pump can fill a tank with water in 2 hours. Because of a leak, it took 4 hours to fill the tank. The leak can drain all the water in ?