Jack usually mows his lawn in 3 hours. Marilyn can mow the same yard in 4 hours. How much time would it take for them to mow the lawn together?

Answer 1

Jack does 1/3 of the job in an hour

Marilyn does 1/4 of the job in a hour

together they do 1/3 + 1/4 = 7/12 job in an hour

7/12 job = 1 job

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1 hour x hours

7/12x = 1

x = 12/7 = 1 5/7 hours