A and B throw one dice for a stake of Rs.11, which is to be won by the player who first throws a six. The game ends when the stake is won by A or B. If A has the first throw, what are their respective expectations?
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Since A throws first, his winning chance is 6/11 versus B's 5/11; multiply each by the Rs.11 stake.
Step 1: A wins on turn k with probability (5/6)^(2(k-1)) x 1/6. Summing this geometric series with first term 1/6 and ratio 25/36: P(A wins) = (1/6) / (1 - 25/36) = (1/6) / (11/36) = 6/11