Math equation for variance

[fauxreigner]

I did not read the thread, because I am lazy. My apologies if this was addressed earlier.

I think you might be interested in a random process called the Poisson Process. It can be used to model random events such as time between radioactive emissions, customer arrivals at stores, or monster spawns in MMORPGs.

Here's a link to some math: http://www.math.uah.edu/stat/poisson/index.html