Let Them Eat Pi
by Pearl Tesler • March 6, 2013
Grab your forks, number crunchers: On March 14 at 1:59 p.m., math lovers round the world will celebrate the irrational number pi by eating pie. But what if cake is more your thing? Not to worry; you can have your cake and celebrate Pi Day, too—by making a Pi Cake.
Rich in mathematical nuance and sweetened by geometry, Pi Cake starts with any cake you feel like eating, so pick your flavor. The magic of Pi Cake actually lies in the decorating of it, with a technique that allows you to use your cake to calculate the value of pi.
Step 1: Bake, buy, or borrow a cake. Round or rectangular, frosted or unfrosted, the choice is yours, but it should have a planar (that’s math-speak for flat) top.
Step 2: Use a straight edge to make a regular pattern of straight, parallel lines across the top of your cake. You can draw these with icing or use a knife to etch lines into an already-frosted cake. Important: The spacing of the lines should exactly equal the length of your toothpicks.
Step 3: Grab a handful of toothpicks (multicolored is more festive) and toss them randomly onto your cake, one at a time. Some toothpicks will miss the cake altogether, while others will extend beyond the outer edge of the cake; collect and remove these stray toothpicks, and leave the rest.
Step 3.14159: Count the total number of remaining toothpicks, multiply by two, and then divide by the number of toothpicks that cross any of your lines. The result, my cake-loving, toothpick-tossing friends, is an approximate value for pi.
Wait a minute—approximate value? Okay, the fine print: If your cake was on the small side or if you skimped on toothpicks, you may wind up with a number closer to 2 or 4. But the more toothpicks you toss, the better the approximation becomes. So if you want a better pi, you may just need a bigger cake.
Craving more pi? Here are other pi activities to try.