A box contains four tickets, numbered 0, 1, 1, and 2. Let Sn be the sum of the numbers obtained from n draws at random with replacement from the box.
a) Display the distribution of S2 in a suitable table.
b) Find P(S50 = 50) approximately.
c) Find an exact formula for P(Sn = k) (k = 0, 1, 2, . . ).