Als produce stand sells 6 tomatoes for $0.90. Barbara’s Produce stand sells 11 tomatoes for $1.54. Which produce stand has the better buy on tomatoes?

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?