Two pipes A and B can separately fill a cistern in 60 min and 75 min respectively. There is a third pipe in the bottom of the cistern to empty it. If all the three pipes are simultaneously opened, then the cistern is full in 50 min. In how much time, the third pipe alone can empty the cistern? -

Two pipes A and B can separately fill a cistern in 60 min and 75 min respectively. There is a third pipe in the bottom of the cistern to empty it. If all the three pipes are simultaneously opened, then the cistern is full in 50 min. In how much time, the third pipe alone can empty the cistern?

A. 90 min
B. 100 min
C. 110 min
D. 120 min
Explanation:
Work done by the third pipe in 1 min = 1/50 – (1/60 + 1/75) = – 1/100.
[-ve sign means emptying]
The third pipe alone can empty the cistern in 100 min.