18th Century French mathematician, Buffon, asked "What is the probability that a needle which falls on the floor, crosses one of the lines between the floor boards?".  It turns out that this number can be used in a Monte Carlo method to approximate π.

We dropped our "needle" 100 times, and got an approximation of 3.22, which is pretty close to 3.14 (considering the small number of trials).

You can read more and find a proof at http://en.wikipedia.org/wiki/Buffon's_needle

I discovered this cool fact on http://io9.com/5862070/find-pi-with-a-sewing-needle which was posted on http://joindiaspora.com