Jeff has a deck of cards: s, s, and s. Armaan randomly draws three cards without replacement. The probability that he takes s can be written as , where and are relatively prime positive integers. Find .
Problem 1320
Official solution
1. First, we need to determine the probability of drawing an on the first draw. Since there are 4 cards out of a total of 12 cards, the probability is:
2. Next, we need to determine the probability of drawing an on the second draw, given that the first card drawn was an . Now, there are 3 cards left out of a total of 11 cards:
3. Finally, we need to determine the probability of drawing an on the third draw, given that the first two cards drawn were both . Now, there are 2 cards left out of a total of 10 cards:
4. The probability of drawing 3 cards in succession is the product of these individual probabilities:
5. The probability that Armaan draws 3 cards can be written as , where and are relatively prime positive integers. Here, and .
6. Therefore, .
The final answer is