Pipe A usually fills a tank in 2 hours. On account of a leak at the bottom of the tank, it takes pipe A 30 more minutes to fill the tank. How long will the leak take to empty a full tank if pipe A is shut?
Choose the correct choice
A) 7 hours	B) 8 hours	C) 9 hours	D) 10 hours	E) 11 hours
Pipe A fills the tank normally in 2 hours. Therefore, it will fill ½ of the tank in an hour.   Let the leak take x hours to empty a full tank when pipe A is shut. Therefore, the leak will empty of the tank in an hour.   The net amount of water that gets filled in the tank in an hour when pipe A is open and when there is a leak = of the tank. — (1)   When there is a leak, the problem states that Pipe A takes two and a half hours to fill the tank. i.e. hours. Therefore, in an hour, of the tank gets filled. – (2)   Equating (1) and (2), we get =&gt; =&gt; x = 10 hours.   The problem can also be mentally done as follows.   Pipe A takes 2 hours to fill the tank. Therefore, it fills half the tank in an hour or 50% of the tank in an hour.   When there is a leak it takes 2 hours 30 minutes for the tank to fill. i.e hours to fill the tank or or 40% of the tank gets filled.   On account of the leak, (50 - 40)% = 10% of the water gets wasted every hour. Therefore, the leak will take 10 hours to drain a full tank.   ANSWER:10 hours
<result>D</result>
Pipe A usually fills a tank in 2 hours. On account of a leak at the bottom of the tank, it takes pipe A 30 more minutes to fill the tank. How long will the leak take to empty a full tank if pipe A is shut?