Friday, March 28, 2008

The Birthday Paradox

This weekend, my children and I are going over the river and through the woods to my nephew’s birthday party. This handsome little man was born on my husband’s birthday 7years ago. Which leads me to ask…with 365 days in a year, how is it that everyone has the same birthday? In my world alone…

My nephew and husband (3/30)
My son and my mom (7/10)
My daughter and my dearest girlfriend (9/9)
Me, the same dearest girlfriends’ husband, and my best friend’s son (2/16)
My niece and the same dearest girlfriend’s son (9/10)
My sister, best friend from childhood, and next door neighbor (6/26)
My husband’s brother and sister – four years apart, I think (2/28)
My best friend’s other son, and the same dearest girlfriend’s daughter (10/26)

It sure creates dilemmas – should each person have their own cake, or do we do one cake with both names? Whose party should we go to? Can we make a party at 10am, 2 pm and 6pm all in one day – all in different towns? Which day are we not going to eat this month so we can buy multiple birthday presents?

As it turns out, I’m not the only person with this problem. There is an entire statistical theory based on it. It’s called the “Birthday Problem” or “Birthday Paradox.” It basically says that in a room of randomly selected people, there is a 50% or greater probability that some of them will share a birthday. http://en.wikipedia.org/wiki/Birthday_paradox

The theory states that in a list of 23 people, if you compare the birthday of the first person on the list to the others, you have 22 chances of success. But if you compare each to the others, you have 253 chances. This is because in a group of 23 people there are 23*22/2=253 pairs, which is more than half of the number of days in the year. So the chance that one of these pairs has a matching birthday is not small. For this reason, along with many others we have the Birthday Paradox. (Courtesy of Wikipedia)

Wow, it’s true – you learn something new everyday. Life really is exciting, even in Kansas.


I wish a happy birthday to my sweet nephew and my darling husband – may there be MANY more. Thanks for giving me two reasons in one day to eat cake.

No comments: