The Smith family has two lawnmowers, one old and one new. Here is a table for how long it takes each son to mow the lawn using each lawnmower and working alone.
Johnny 2 hrs 2 hrs 30 min
Jimmy 3 hrs 3 hrs 40 min
How long does it take them working together:
a. If Johnny uses the new one and Jimmy uses the old one?
b. If Johnny uses the old one and Jimmy uses the new one?