First Ace at Card 14

Probability
Cards
Medium
A shuffled standard deck is revealed one card at a time. What is the probability that the first ace appears exactly as card 14?
Hint 1

The first 13 cards must be non-aces and card 14 must be an ace.

Hint 2

Think of it via order statistics: choose positions of the 4 aces among 52 cards.

Show worked solution
  1. 1. Reframe with combinations

    The event happens if and only if exactly one of the 4 aces is in position 14, and the other 3 aces along with the choice of positions of all 4 aces among the first 13+the rest matter; equivalently, condition on positions of the 4 aces among 52 slots.

  2. 2. Direct combinatorial count

    The first ace is at position 14 if and only if positions 1–13 contain no ace (all from the 48 non-aces) and position 14 is an ace. Equivalently choose the 3 remaining aces to be among the remaining cards.

  3. 3. Interpretation

    This matches choosing which 4 of 52 positions hold aces, conditioned so that the smallest is position 14: the other 3 ace positions are chosen from the 38 positions after 14, and positions 1-13 are automatically non-ace.

Answer: C(38,3) / C(52,4)

Related roles: Browse quant jobs

Related problems