If you flip a coin, and it comes up heads twenty times in a row, the next flip will be heads.

by phil on Friday May 21, 2010 2:07 AM

If a coin-flip turns up heads 20 times in a row, what is the next flip going to be? Heads, clearly. You could say that there's a 50-50 chance that it will be heads or tails, but with that much consecutivity, the odds are extremely high that something is wrong with the system instead (like a fake coin). If the interviewer then added, "assume the coin is honest," I'd still say something is wrong with the system (maybe a robot is flipping the coin in exactly the same way each time). Eventually, your interviewer would get frustrated and blurt out, "OKAY FINE, Assume there's a 50-50 chance it will appear heads," and then the conversation is over.

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