386.An Even Number of Flips
★★★classical probabilityCh. 2 — Axiomatic and Conditional Probability444+ Problems in Probability
Ahmed flips a fair coin until he obtains two consecutive identical outcomes (HH or TT) for the first time. What is the probability that Ahmed flips the coin an even number of times?
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Stopping at flip means the first flips strictly alternate. What's the probability of that?
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