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5986概率中等derivationmedium

Expected Winnings Over a Random Number of Bets

题目

A gambler places bets until a random stopping rule halts play; the number of bets NN is a stopping time for the i.i.d. bet outcomes with E[N]=8E[N]=8. Each bet has an i.i.d. net result XiX_i with E[Xi]=0.05E[X_i]=-0.05 (a 5%5\% house edge per unit staked, with unit stakes), and the decision to stop after bet nn depends only on outcomes up to bet nn. Compute the gambler's expected total winnings E ⁣[i=1NXi]E\!\left[\sum_{i=1}^N X_i\right], and state whether any stopping rule with E[N]=8E[N]=8 can make this positive.

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你的答案

expected total winnings

can be positive