A cistern which could be filled in 4 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?  Pick:
A) 76 hrs
B) 99 hrs
C) 55 hrs
D) 20/3 hrs
E) 11 hrs
1/4 - 1/x = 1/10   =&gt; 20/3 hrs   Answer: 20/3 hrs
<result>D</result>
A cistern which could be filled in 4 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?