Question

It takes a new mail carrier 4 hours to deliver the mail on route a. It takes an experienced mail carrier 3 hours to do the same job. How long would it take if they worked together?

Answer 1

Answer:
`(12)/(7)\ \text{hours}`

Explanation:

Given

New mail carrier takes 4 hours for delivery i.e.

New mail carrier completes
`(1)/(4)` part of work in 1 hour

Old mail carrier takes 3 hours for delivery i.e.

mail carrier completes
`(1)/(3)` part of work in 1 hour

If they work together, they complete the work in x hours i.e.

`\Rightarrow (1)/(x)=(1)/(4)+(1)/(3)\\\Rightarrow (1)/(x)=(3+4)/(12)\\\Rightarrow x=(12)/(7)\ \text{hours}`