One painter can paint a house in 12 hours another can paint the house in 8 hours, how long will it take for both of them to paint 1 house

4.8 hours. 

You can get this by setting up the equation:
x/8 + x/12 = 1
Where x is equal to the amount of hours spent working. In this equation x/4 would be the first painter. In 8 hours he would paint on room. x/12 would be the second painter. When you add them together using common denominators, you can find x.