Pipe A can fill a tank in 60 min . There is a second pipe in the bottom of the cistern to empty it. If all the two pipes are simultaneously opened, then the cistern is full in 180 min. In how much time, the second pipe alone can empty the cistern?
Options.
A) 60 min	B) 45 min	C) 90 min	D) 70 min	E) 30 min

Rationale: work done by the third pipe in 1 min = 1 / 180 - ( 1 / 60 ) = - 1 / 45 . [ - ve sign means emptying ] the third pipe alone can empty the cistern in 45 min . answer : b
Answer: B