Question

Jack usually mows his lawn in 5 hours. Marilyn can mow the same yard in 7 hours. How much time would it take for them to mow the lawn​ together?

Answer 1

`approx 2.92` hours
`approx 2` hours `55` mins

Explanation:

If Jack can mow his lawn in `5` hours, it means that we can mow `1/5` of his lawn in `1` hour.

Similarly, Marilyn can mow `1/7` of the same lawn in `1` hour.

So, together, they can mow `1/5+1/7 = 12/35`

This means that after `t` hours they can mow `12/35 t` lawns.

We want to know how many hours it takes them to mow one lawn, so we want to solve

`12/35 t = 1`

and thus

`t = 35/12 approx 2.92`

And `2.92` hours are approximately `2` hours and `55` minutes.