Posted by anxious on Monday, May 4, 2009 at 9:35pm.
In 30 hours, Jack mows 5 lawns, and Marilyn can mow 6 lawns.
That is 11 lawns in 30 hours.
rate=11/30 lawns/hr.
so one lawn will take 30/11 hrs.
Jack's rate = job/6
Marilyn's rate = job/5
their combined rate = job/6 + job/5
= 11job/30
job = rate x time
so time for combined effort = job/rate
= job/(11job/30)
= 30/11
So it takes 30/11 hours
= 2 8/11 hours
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