A box initially contains 1 RED ball and 2 WHITE balls all the same size. You select a ball at random and then return it to the box together with another ball of the same colour. The box now contains four balls. Again you select a ball at random from the box. Find the probability that both selected balls are the same colour.
What I think:
red/red + white/white = (1/3*2/4)+(2/3*3/4)