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?

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Answer 1 · 2018-06-21T08:11:24

#approx 2.92# hours
#approx 2# hours #55# mins

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.

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?