math/117
posted by Angela .
Jack usually mowes his lawn in 7 hours. Marilyn can mow the same yard in 4 hours. How musch time would it take for them to mow the lawn together?

3 hrs

jack mows (1/7) lawn per hour
marilyn mows (1/4) yard per hour
together they mow 1/7 + 1/4 yard per hour
= 4/28 + 7/28 = 11/28 yards per hour
so
28/11 = about 2.54 hours/yard 
Which one is the answer? 3 or 2.54?

Damon's answer is correct.