How to Make an Honest Coin Flip From a Bad Coin
The coin toss, the final 50-50 pick, is actually a bit biased. According to a study by Stanford University , the probability that even an honest coin will fall to the same surface it was launched on is roughly 51%. And if you spin rather than toss, even a lightly weighted coin is much more likely to fall to the heavier side. (80% of the time, a coin that is rolled goes upside down.) But there is a cool math trick to get a fair result from an unfair coin.
The Fermat Library’s Twitter account , a collection of mathematical and scientific curiosities, posted a simple solution : instead of choosing heads or tails, choose between heads and tails. As long as you do the same flip every time, the probabilities of HT and TH are equal.
Using this technique, you can flip almost any object that can land from two different sides, no matter how often it lands from one side to the other. Or really any random binary process that you can’t influence.
Follow Fermat’s library for smarter math tricks like how to fold any circle into an ellipse , or a cheat sheet for all trigonometric functions .