From a standard deck of 52 cards, five cards (called a hand) are randomly selected. (a) What is the probability that the hand contains exactly two aces? (b) What is the probability that the hand contains three-of-a-kind (but not four- of-a-kind nor a full house)? Three-of-a-kind means three cards with the same rank, such as 444. A full house is a hand consisting of three-of-a-kind and a pair.