An electric pump can fill a tank in 3 hours. Because of a leak in the tank, it took 3 hours 30 min to fill the tank. In what time the leak can drain out all the water of the tank and will make tank empty ?
Pick one
A) 10 hours	B) 13 hours	C) 17 hours	D) 21 hours	E) 25 hours
Explanation:   We can get the answer by subtrating work done by leak in one hour by subtraction of filling for 1 hour without leak and with leak, as   Work done for 1 hour without leak = 1/3   Work done with leak = 3 1/2=7/2   Work done with leak in 1 hr=2/7   Work done by leak in 1 hr=1/3=2/7=1/21   So tank will be empty by the leak in 21 hours.   ANSWER IS 21 hours
<result>D</result>
An electric pump can fill a tank in 3 hours. Because of a leak in the tank, it took 3 hours 30 min to fill the tank. In what time the leak can drain out all the water of the tank and will make tank empty ?