At a party hosted by the Shannons, young Peggy Shannon was in charge of the toothpicks. She was carrying a box of them on the house’s verandah—and then dropped it by accident, spilling its contents onto the porch. Her father, standing nearby, paused, took stock of the mess, and then said, “Did you know, you can calculate pi with that?” He was referring to Buffon’s Needle, a famous problem in geometric probability: it turns out that when you drop a series of needles (or toothpicks) on an evenly lined floor, the proportion of needles falling across a line can be used to estimate pi with
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