Question

A bath can be filled by the cold water pipe in 10 min and by hot water pipe in 15 min (independently each). a person leaves the bathroom after turning on both pipes simultaneously and returns at the moments when the bath should be full. finding, however, that the waste pipe has been open he now closes it. in 4 min more, bath is full. in what time would be the waste pipe empty it?

Answer 1

8minutes only is the ans