Question 254740
Sally can paint a house in 4 hours 

that means in 1 hour sally can paint 1/4 th of the house
similarly  in 1 hour john can paint 1/6 th of the house

so together in 1 hour they can paint 1/4 + 1/6 = 5/12 th of the house

so to paint the house together they take 12/5 hours

that is 2.4 hours