Expected cards turned until an ace shows
Question
A standard -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
. The four aces split the other cards into five gaps that are equally large on average, so the gap before the first ace has mean . Adding the ace itself gives .
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Open the worked solutionLessons behind this question
- Expectation, Mean, and Variance
- Conditional Expectation and Variance Revisited
- Sample Spaces, Events, and the Probability Axioms
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