alt Hacker NewsEasy 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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I’ve seen this attributed to John von Neumann, of all people
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.
Each flip would need to start with the same side up though, if this paper is correct.
What if consecutive unfair coin flips are not independent?
If anyone wants to look up why this might work, it's a Whitening transform [0]. I can't find the name of the algorithm itself being describe in the parent but there's more than just that for accomplishing the same thing.
0: https://en.wikipedia.org/wiki/Whitening_transformation