A total of 2 feet of snow falls over three days. On the first day, 1/6 of the total snow falls. On the second day, 7/12 of the total snow falls.

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?