SOLUTION: Jack can mow a lawn in 5hrs. Mary can more the same lawn in 4 hrs. How long will it take for them to mow the same lawn together.

Question 330519: Jack can mow a lawn in 5hrs. Mary can more the same lawn in 4 hrs. How long will it take for them to mow the same lawn together.
Answer by mananth(16946) (Show Source): You can put this solution on YOUR website!
Jack takes 5 hours
so he can do 1/5 of the job in 1 hour
,,
Mary can do it in 4 hours
so she does 1/4 of the job in 1 hour
..
Together they will do 1/5 + 1/4 of the job in 1 hour.
LCD = 20
4+5 / 20
=9/20 of the job in 1 hour
..
they will take 20 / 9 hours to do the job
=2.22 hours
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