By George Hart for the Museum of Mathematics


There are many ways to calculate an approximation to pi, but rarely is math as delicious as in this idea from Davidson College professor Tim Chartier. Make a quarter circle in a square of graph paper and place chocolate chips on the squares that lie completely inside the circle. If you now count the chips and compute four times the number of chocolate chips divided by the total number of squares, that will be approximately pi. Here, there are 22 chips out of 36 squares, so we calculate 4∙22/36=2.444, which is off by about 0.7 from 3.14, so is not a very close estimate of pi, but we can improve it.

But if you are willing to invest in more chocolate, you will get a better answer. In the 11×11 grid below, you can count 83 chips, giving a somewhat better approximation of 4∙83/121=2.74.

For an even better approximation, you’ll want to have a group of helpers. Tim and friends counted 2232 chips in a 54×54 grid, resulting in an approximation of 3.06, which is getting pretty close to pi. The best thing about this chocolate calculation is that it is sure to end with a pi eating event. The full report is here.

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