Un-biasing a biased coin

Puzzle: You and a friend are sharing a car. Neither of you wants to drive. Your friend suggests you flip a coin for it, and offers up a coin. You suspect it might be biased. How might you still use the coin to ensure a fair decision?

Answer: Flip the coin twice. Instead of deciding between heads and tails, decide between HT and TH. These outcomes are equally likely, since the two flips are independent. If you get HH or TT, just flip again.

Originally published on Medium.

What can computers do? What are the limits of mathematics? And just how busy can a busy beaver be? This year, I’m writing Busy Beavers, a unique interactive book on computability theory. You and I will take a practical and modern approach to answering these questions — or at least learning why some questions are unanswerable!

It’s only $19, and you can get 50% off if you find the discount code ... Not quite. Hackers use the console!

After months of secret toil, I and Andrew Carr released Everyday Data Science, a unique interactive online course! You’ll make the perfect glass of lemonade using Thompson sampling. You’ll lose weight with differential equations. And you might just qualify for the Olympics with a bit of statistics!

It’s $29, but you can get 50% off if you find the discount code ... Not quite. Hackers use the console!

More by Jim

Tagged . All content copyright James Fisher 2013. This post is not associated with my employer. Found an error? Edit this page.