That’s easy. Let’s say you wanted to know how big a tire to get for your bike. You know that the diameter of your wheel is 28inches, but you don’t know it’s circumference.

Well, then, you can just go out on the street or to a mall or something. Anywhere where there’s a bunch of strangers.And ask each person to pick two random positive integers.For each pair of integers, you determine whether they are relatively prime ( if any integer larger than 1 divides them both then they aren’t relatively prime) Anyway, you keep a track of the total number of pairs you have collected, and how many of them were relatively prime. As soon as you are tired of this you go back home. Then you take the total number of pairs, multiply it by six. Divide that by the total number that were relatively prime. Then take the square root. Now, you take the result of that and multiply it by 28 inches (the diameter of the wheel). And the result will be the circumference.

This is true.

Of course, this involves randomness, statistics, so accuracy isn’t absolute. But if you even just collected a couple of hundred pairs your result would probably be as accurate as if you used a tape measure.

I love this fact.