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Payout from blue beating red by three before a tie

Question

A red and a blue fair ten-sided die (faces 11–1010) are rolled together repeatedly. When the two match, the game stops. Otherwise, if blue exceeds red by 33 or more you earn $1, and in every non-matching case you roll again. What is your expected total winnings?

Short answer

14/514/5. Per round, a tie has probability 110\tfrac1{10} and a paying outcome 28100\tfrac{28}{100} (red =k=k allows 8−k8-k blue values, k≤7k\le7). The number of rounds is geometric, so expected earnings are 0.280.1=2.8\tfrac{0.28}{0.1}=2.8.

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

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