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392 points seanhunter | 4 comments | | HN request time: 0.629s | source
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NameError ◴[] No.42184405[source]
Easy way to get a fair result from an unfair coin toss: Flip the coin twice in a row, in this case starting with the same side facing up both times, so it's equally unfair for both tosses. If you get heads-heads or tails-tails, discard and start over until you get either heads-tails or tails-heads, which have equal probabilities (so you can say something like HT = "heads" and TH = "tails").

This works even if the coin lands heads 99% of the time, as long as it's consistent (but you'll probably have to flip a bunch of times in that case).

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1. mankyd ◴[] No.42184523[source]
Importantly - you don't have to know the odds of the coin ahead of time, or which side is more likely. You only need to know that it is consistent.
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2. IncreasePosts ◴[] No.42184778[source]
The odds are important to know because if someone gave you a trick coin that always lands on heads, you will be flipping coins until the end of the universe. And I'm sure you have more important things to do than that.
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3. Vecr ◴[] No.42184898[source]
Nah, you can put in a rule to stop. It would be better to know ahead of time, but you don't need to.
4. magicalhippo ◴[] No.42184924[source]
> you will be flipping coins until the end of the universe

Reminds me of one of my favorite movies, Rosencrantz & Guildenstern Are Dead, which opens with just such a scenario[1].

[1]: https://www.youtube.com/watch?v=RjOqaD5tWB0