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The 1000-Coin Conundrum

Medium · Game Theory & Logic · Quant Trader interview question · probability, bayes-theorem, mental-math, conditional-probability

You are presented with 1000 coins. 999 are fair, and 1 is a double-headed coin (two heads). You randomly select one coin from the pile and flip it 10 times, observing 10 heads in a row. What is the approximate probability that you selected the double-headed coin?