What is the final step to prove that Sn 1 + 2 + 3 + ... + n = n(n+1)/2? a. Verify that Sn is valid for n = 1 c. Assume that Sn is valid for n = k b. Show that Sn is valid for n = k d. Prove that Sn is valid for n = k + 1

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?