Question

A bath tub can be filled by the cold water pipe in 40 minutes and by the hot water pipe in 60 minutes. A person leaves the bathroom after turning on both pipes simultaneously and returns at the moment when the bath should be full. Finding, however, that the waste pipe has been open, he now closes it. In 12 minutes more the bath tub is full. In what time would the waste pipe empty it?

Answer 1

The cold water pipe can fill in 20 minutes

The hot water pipe can fill in 30 minutes.

so,the cold water pipe can fill the bath in one minute is 1/20

so,the hot water pipe can fill the bath in one minute is 1/30.

both can fill the bath in one minute= 1/20+1/30

= 3+2/60

= 5/60

= 1/12

so, they can fill in 12 minutes