SOLUTION: Hi story problems are not favorite and seem to get confused with them. Can you please help me with this one. Jack usually mows his lawn in 3 hours. Marilyn can mow the same yard

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Question 340940: Hi story problems are not favorite and seem to get confused with them. Can you please help me with this one.
Jack usually mows his lawn in 3 hours. Marilyn can mow the same yard in 7 hours, how much time would it take for them to mow the lawn together?

Thanks :o)
Answer by nerdybill(7384) About Me  (Show Source):
You can put this solution on YOUR website!
Jack usually mows his lawn in 3 hours. Marilyn can mow the same yard in 7 hours, how much time would it take for them to mow the lawn together?
.
Let x = hous it takes for both to mow lawn
then
x(1/3 + 1/7) = 1
Multiplying both sides by 21:
x(7 + 3) = 21
x(10) = 21
x = 2.1 hours
or
x = 2 hours and 6 minutes