Jay and his brother Ray own a janitorial service. Jay can do a cleaning job alone in 5 hours and Ray can do the same job in 4 hours. How long will it take them to do the job together?

Solution:

The time they do together is x

So

1/x=1/4+1/5

x=20/9 = 2.22

So it takes 2.22 hours to do the job together