Expected smallest roll seen before the first five
Question
A fair die is rolled repeatedly, stopping as soon as a appears. Taking all rolls into account, including the final , what is the expected value of the smallest number rolled?
Short answer
. The minimum is exactly when appears before the first , which in turn comes before every value below . By symmetry among first appearances this has probability , and the minimum is with probability . So .
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Open the worked solutionLessons behind this question
- Expectation, Mean, and Variance
- Counting and Combinatorics
- Conditional Expectation and Variance Revisited
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