Approximating π by throwing darts

We can approximate π using nothing more than random numbers and some simple geometry: we draw a square with side 2r around a circle with radius r, then we randomly throw darts at it. We count all of the 'throws'; if a dart lands within the circle, we also count a 'hit'.

For a large number of throws, we see that:

Some half-remembered maths tells us that:

Or:

I first solved this problem as an undergraduate sometime in 1994 as part of a Computational Physics module. Using FORTRAN 77.

Note: each blob having a different radius is completely irrelevant to the process, it just makes a nicer image.