Choosing which consecutive die pair to wait for
Question
(Answer by intuition, without writing anything down.) A fair die is rolled repeatedly until a chosen ordered pair of values appears on two consecutive rolls, and you are paid one unit per roll made. Which target should you prefer: (1) a followed by a , (2) a followed by another , or (3) does it make no difference? Give the case number.
Short answer
Case 2. Both targets need a 4 first. In the 4-then-5 game, a failed attempt that rolls another 4 still leaves you one roll from finishing, whereas in the 4-then-4 game every failure after a 4 sends you back to the start. So 4-4 takes longer on average (42 rolls versus 36), which is what you want when paid per roll.
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Open the worked solutionLessons behind this question
- Conditional Expectation and Variance Revisited
- Counting and Combinatorics
- Expectation, Mean, and Variance
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