Privileges that aliens do not enjoy

Brent wants to know what is 5 x 1/2

There are three bags: a (contains 2 white and 4 red balls), b (8 white, 4 red) and c (1 white 3 red). you select one ball at random from each bag, observe that exactly two are white, but forget which ball came from which bag. what is the probability that you selected a white ball from bag a?

What function has a range {yly< 5}? question on picture above^