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).

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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