Question

Two pipes 'A' and 'B' can separately fill a cistern in 20 min and 25 min respectively, while a third pipe 'C' can empty the cistern in 15 min. How long will it take to fill the cistern, if all the pipes are opened simultaneously?
(a) 34 min
(b) 39 min
(c) 48 min
(d) 43 min​

Answer 1

thirty nine is the answer