383.Convincingly Double-Headed
★★★conditional probabilityCh. 2 — Axiomatic and Conditional Probability444+ Problems in Probability
A bag has 19 fair coins and 1 double-headed coin. You pick a coin uniformly at random and flip it. What is the minimum number of consecutive heads you must observe before the coin is more likely than not to be the double-headed one?
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After heads, compare the prior odds against the likelihood ratio .
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