December is cold and dark enough that I don't spend much time out in my garden. Sure, I'm still picking salad greens, and planted garlic and fava beans yesterday - better late than never. I'm also still picking tomatoes, and plan to make a green salsa later this week. But as a break today we're going to talk about the birthday conundrum instead of the backyard vegetable plot.
We've all been to a potluck where somebody else shares a birthday with another guest. If 23 people gather together, chances are fifty fifty that two share the same birthday. Raise the number of folks to sixty, and you're 99 percent sure of having a shared birthday in the group - even though there are 365 options available - more if you throw in February 29th.
And your potluck cohort isn't the first group to notice this surprising occurrence.
"You say it's your birthday. It's my birthday too yeah."
The simplest non mathematical way of seeing why shared birthdays are so common comes by examining the extreme case. 365 people without a shared birthday would be an expectedly rare occurrence indeed.
Here's a link to wikipedia's mathematical explanation which involves the use of factorials and other less common math techniques for those who want to prove your sense of surprise rather than just be awed by it.
All these calculations assume each day has the same number of people born on it - which is not true. September 9th is the most common birthday - shared by Leo Tolstoy, Hugh Grant, and Colonel Sanders among others - maybe you too.
And if yours is December 2nd - today - happy birthday.
