Pigeons

First and foremost, this blog is amazing and you should check it out. While checking it out myself, I was reminded of a simple, but cool concept. The Pigeonhole Principle. I'm going to use an example similar to the one on the blog.

Suppose there are 11 pigeons trying to roost in 10 pigeonholes. At least one of those holes is going to end up with 2 or more pigeons. Sounds obvious right? What if I told you there are at least two (non-bald) people in Seattle, Washington with the same number of hairs on their head? Doesn't sound so obvious, but that's exactly why the pigeonhole principle is cool!

Most, if not all people, have fewer than 200,000 hairs on their head. There are more than 600,000 people living in Seattle. There are more people (pigeons) than possible numbers of hairs (pigeonholes). The same is true for any city with enough people.