Question

A new type of pump can drain a certain pool in 7 hours. An older pump can drain the pool in 13 hours. How long will it take both pumps working together to drain the pool?

Answer 1

Both the pumps together will drain the pool in 4.55 hours.

Explanation:

Pool can be drained by a new pump in the duration = 7 hours

Older pump can drain the pool in the time = 13 hours

Per hour capacity of the new pump to drain the pool =
`(1)/(7)` part of the pool

Per hour capacity of the older pump =
`(1)/(13)` part of the pool

When both the pumps work together then part of the pool drained in one hour =
`(1)/(7)+(1)/(13)`

=
`(7+13)/(91)`

=
`(20)/(91)`

Since
`(20)/(91)` part of the pool is drained in the time = 1 hour,

therefore full pool will be drained in the duration =
`(1)/((20)/(91) )`

=
`(91)/(20)`

= 4.55 hours