Puzzles/Statistical puzzles/Buffon's needle
This is a classic puzzle attributed to Buffon. Here it is:
Assume you stand on a floor with a pattern of parallel lines on it which are spaced at unit distance. Now you throw a needle of length D with D < 1. What is the probability that the needle intersects one of the lines?
This puzzle assumes ideal lines and needle of extend zero.
The solution is given in Wikipedia.