posted by Anonymous J on .
Jack usually mows his lawn in 6 hours. Marilyn can mow the same lawn in 7 hours. How long would it take if they were both working together?
Jack's rate = lawn/6
Marilyn's rate = lawn/7
combined rate = lawn/6 + lawn/7 = 13lawn/42
combined time = lawn/(13lawn/42) = 42/13 or 3.23 hours
it would take about 2 hours and 14 minutes.