I’d like anyone who was born on March 22nd to stand up.” Two students stand up. They link eyes from across the room, and smile. The room laughs. “Now… - David Franklin

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I’d like anyone who was born on March 22nd to stand up.” Two students stand up. They link eyes from across the room, and smile. The room laughs. “Now, anyone born on June 14th.” Another two stand up. The room laughs again. “Now, anyone born on August 2nd.” Two more: the class is laughing at each pair, and re-examining their original takes on how low the probability was likely to be. They are learning through experience about human fallibility with estimating probabilities, and at the same time learning something about their classmates. “How about December 21st?” This time, three students stand up. This gets a big laugh for two reasons: firstly, it is unexpected, and secondly, it helps to ram home the idea that in a class that size (there are about 3,000 pairs in a class of 80), there are likely to be “coincidences” everywhere.