A pump can fill a tank with water in 3 hours. Because of a leak, it took 7 hours to fill the tank. The leak can drain all the water in ?  Pick one.
A) 15hr 10min  B) 16hr 20min  C) 5hr 15min  D) 15hr  E) 14hr 25min
Work done by the leak in 1 hour = 1/3 - 1/7 = 4/21   Leak will empty the tank in 21/4 hrs = 5hr 15min   Answer is 5hr 15min
<result>C</result>
A pump can fill a tank with water in 3 hours. Because of a leak, it took 7 hours to fill the tank. The leak can drain all the water in ?