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

Answer 1

Each hour Jack mows 1/4 of the lawn.
Marilyn mows 1/3 of the lawn.

Together, each hour they mow 1/4+1/3=7/12 of the lawn.
How long would it take to mow the whole lawn:
x/1 = 7/12
Cross multiply to find x.