Throw needles at random onto paper ruled with evenly spaced lines. If you know only the proportion of needles that cross a line, π surprisingly emerges from this experiment, which seems to have nothing to do with circles. The experiment was first conceived by the French Count of Buffon in 1777.
Formula: If the needle length is L and the line spacing is d (L≤d), the probability that the needle crosses a line is exactly 2L/(πd). So if you throw N needles and H of them cross a line, you can estimate π in reverse using π ≈ 2LN/(dH). The more needles you throw, the more accurate the estimate becomes.
Needles thrown 0Needles crossing a line 0Estimated π ≈ -
The actual value of π is 3.14159... Watch to see whether the estimate gradually approaches this number as you increase the number of needles.