15. In a deck of cards, there are 52 cards split evenly between red suits (hearts and diamonds) and black suits (clubs and spades). In each suit, there are cards numbered 2 through 10 , a jack, a queen, a king and an ace. What is the probability that the card on the top of the deck is an ace?

Step 1 ：In a deck of 52 cards, there are 4 aces.

Step 2 ：We are asked to find the probability that the card on the top of the deck is an ace.

Step 3 ：The probability of an event is calculated by dividing the number of favorable outcomes by the total number of outcomes.

Step 4 ：In this case, the favorable outcome is drawing an ace, and there are 4 aces in the deck.

Step 5 ：The total number of outcomes is the total number of cards in the deck, which is 52.

Step 6 ：So, the probability \( P \) is calculated as follows: \( P = \frac{aces}{total\_cards} \)

Step 7 ：Substituting the given values, we get \( P = \frac{4}{52} \)

Step 8 ：Simplifying the fraction, we get \( P \approx 0.077 \)

Step 9 ：\(\boxed{0.077}\) is the probability that the card on the top of the deck is an ace.