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Probability

Three steps, all forward?

random-walkcountingcoin-flips

A token starts at 0 and takes 3 steps. Each step is +1+1 or −1-1, each with probability 1/21/2, independently.

What is the probability the token ends at +3+3?

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Balls and Bins and the Birthday ProblemBinomial Coefficients and Pascal's TriangleBurnside's Lemma and Polya CountingCatalan NumbersCounting: Permutations and Combinations

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