Jack usually mows his lawn in 3 hours. Marilyn can mow the same yard in 5 hours. How long would it take them to mow the lawn together?

Answer 1

Jack's rate alone = 1/3
Marilyn's rate = 1/5
combined rate = 1/3 + 1/5 = 8/15

time at combined rate = 1/(8/15) = 15/8 = 1.875 hrs
or 1 hour and appr 53 minutes

Answer 2

4 hours