A cistern which could be filled in 9 hours takes one hour more to be filled owing to a leak in its bottom. If the cistern is full in what time will the leak empty it?	Choose one:
A) 27 hrs	B) 29 hrs	C) 28 hrs	D) 90 hrs	E) 98 hrs
1/9 - 1/x = 1/10   =&gt; 90 hrs   Answer:90 hrs
<result>D</result>
A cistern which could be filled in 9 hours takes one hour more to be filled owing to a leak in its bottom. If the cistern is full in what time will the leak empty it?