If sally can paint a house in 4hrs, and John can paint the same house in 6hrs, How long will it take for both of them to paint the house together?
Sally's rate = house/4
Johns rate = house/4
working together = house/(house/4 + house/6)
= house/(10house/24)
= house * 24 10house
= 24/10 = 2.4
it will take 2.4 hrs or 2hrs, 24 minutes