Monday, March 21, 2011

The Tim Hortons School of Probability

Do you know what this object is? We've just come to the end of that late-winter Canadian ritual when we line up to buy coffee, hoping for the magic words: "Win donut / Gagnez un beigne".

There are a couple of neat posts here and here, using "roll up the rim" to illustrate the binomial distribution. But you can also use it to illustrate the geometric distribution.

The geometric distribution (GD) gives a distribution on the number of trials before the next win. It's like the binomial distribution (BD) for impatient people: The BD asks, "If I buy 20 coffees, how many prizes can I get?" while the GD asks, "How many coffees do I have to buy until I get my next prize?"