Erin had 55 stuffed bears. she took out her favorite 7 bears and then equally divided the other bears among her 3 sisters. erin's youngest sister, su, already had 15stuffed bears. how many stuffed bears does su have now?

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?