There are 4 different types of coupons, the first 2 of which compose one group and the second 2 another group. Each new coupon obtained is type I with probability pi, where p1 = p2 = 1/8, p3 = p4 = 3/8. Find the expected number of coupons that one must obtain to have at least one of
(a) All 4 types;
(b) All the types of the first group;
(c) All the types of the second group;
(d) All the types of either group.