Question 18846
You can start by finding the rate (how much per hour) at which Sally and John can paint.

If Sally can paint the entire house in 4 hours, then she can paint 1/4 of the house in 1 hour.
If John can paint the entire house in 6 hours, then he can paint 1/6 of the house in 1 hour.

Together, they can paint (1/4 + 1/6 = 3/12 + 2/12 = 5/12) of the house in 1 hour.

You could make a little equation from this, where H = the house:
 (5/12)H  = 1 hour.
 To find 1 H, you would multiply both sides by the multiplicative inverse of 5/12, that's 12/5.


H = 12/5 hours

So, together they can paint the entire house in 12/5 hrs. = 2 2/5 hrs. = 2 hours 24 minutes.