Birthday Probability

Joe Carter at the Evangelical Outpost refers to what he calls the “birthday paradox,” which really means that it’s surprisingly likely that two in a group of people will share the same birthday.

I once worked with a professor who exploited this for his own amusement and the class’s education. He’d offer to make a wager with someone from the lecture hall of sixty students: if there were no two people with the same birthday, he’d give that person the course textbook (an over $100 value), but if there were, that person would have to give him $10.

Someone always took him up on it, and as far as I know, he never had to give away his book (but he also didn’t accept the $10, either), because the probability for sixty people is around 95%, if I remember correctly.


  1. who was that professor and where were lori hansen and i? we found out in our german conversation class back in ’97(i don’t think there were more than 15 in that class) that we have the same birthday. same day. same year.

    my boss and i also have the same birthday. he’s just 40 years my senior. one of my former students has my birthday too.

  2. It was a professor in a probability course at USC.

    That’s a lot of people sharing your birthday, melanie. I don’t think I know that many who share mine, but one who does was my best friend and best man in my wedding.

  3. oh, and i just remembered that i know of 3 couples who share the same birthday as well.

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