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Guessing a deck of three aces and three jacks

Question

A face-down pile contains exactly 33 aces and 33 jacks in random order, and Jamie knows this. Cards are turned over one at a time; before each card is revealed Jamie guesses whether it is an ace or a jack, winning $1\text{\char36}1 for each correct guess. Playing all 66 cards optimally, how much does Jamie expect to win?

Short answer

$4.10\text{\char36}4.10. Always guess the type with more cards remaining (either on a tie). By backward induction, or by summing the turn-by-turn success probabilities 12,35,35,710,710,1\tfrac12,\tfrac35,\tfrac35,\tfrac{7}{10},\tfrac{7}{10},1, the expected total is 4110\tfrac{41}{10}.

Adapted from QuantQuestions.io; question and answer rewritten by SelfMadeQuant.com.

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