What is the prime factorization of 72?
a. 2.2.2.3

b. 2.2.2.5

c. 2.2.3.3.3

d. 2.2.2.3.3

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?