math
posted by thommini .
If Sally can paint a house in 4 hours, and John can paint the same house in 6 hour, how long will it take for both of them to paint the house together?

In 12 hours, Sally paints 3
in 12 hours, John paints 2
so the together rate is 5 houses/12 hrs
so together 12hrs/5houses= 2.4 hrs/house