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Expected cards turned until an ace shows

Question

A standard 5252-card deck is shuffled and you turn cards face up one at a time from the top. What is the expected number of cards you turn over up to and including the first ace?

Short answer

53/5=10.653/5 = 10.6. The four aces split the 4848 other cards into five gaps that are equally large on average, so the gap before the first ace has mean 48/548/5. Adding the ace itself gives 48/5+1=10.648/5+1=10.6.

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

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