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Birthday Surprises

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Author:Ivars Peterson (MathTrek)
Description: It's rather unlikely that you and I share the same birthday (month and date). The more people you pull into the group, however, the more likely it is that at least two people will have matching dates. Ignoring the minor technicality of leap years, it's clear that in a group of 366 people, at least two must share a birthday. Yet it seems counterintuitive to many that only 23 people are needed in a group to have a 50-50 chance of at least one coincidental birthday. To see why it takes just 23 people to reach even odds on sharing a birthday, you have to look at the probabilities...

Levels: Middle School (6-8), High School (9-12), College
Languages: English
Resource Types: Articles
Math Topics: Calendars/Dates/Time, Probability

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