Question 615414
Jack usually mow his lawn in 4 hours. Marilyn can mow the same yard in 3 hours. How much time would it take for them to mow the lawn together? 
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Let x = time (hours) if they mowed lawn together
then
x(1/4 + 1/3) = 1
multiplying both sides by 12:
x(3 + 4) = 12
x(7) = 12
x = 12/7 hour
or 
x = 1 hour and 43 minutes