Suppose that a needle of length l is dropped at random onto a set of parallel lines a distance d apart, where l < d. The probability that the needle lands crossing one of the lines can be shown to equal 2l/(π‎d). The experiment in which this is repeated many times to estimate the value of π‎ is called Buffon’s needle. It was proposed by Georges Louis Leclerc, Comte de Buffon (1707–88).

http://www.mste.uiuc.edu/reese/buffon/bufjava.html A simulation of Buffon’s needle experiment.