65.One Coin in a Thousand
★★★conditional probabilityHudson River Trading
A jar holds 1000 coins, of which exactly one is double-headed and the other 999 are fair. You draw a coin at random and flip it 10 times, getting heads every time. What is the probability that you drew the double-headed coin?
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Compare how likely each type was to produce ten straight heads. The trick coin does it every time; a fair coin manages it once in 1024 attempts.
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