Back-to-back heads with coins of bias 1 over k
Question
Kevin tosses coins in order, where coin lands heads with probability . He earns for every pair of adjacent coins that both show heads, with overlaps counting separately (so HHH earns ). If is his expected earnings with coins, find (enter if it does not exist).
Short answer
. By linearity, the expected payout is the sum over adjacent coin pairs of the chance both show heads, . The sum telescopes to , which tends to .
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Open the worked solutionLessons behind this question
- Expectation, Mean, and Variance
- Conditional Expectation and Variance Revisited
- Indeterminate Forms and L'Hôpital's Rule
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