Friday, March 02, 2007

Birthday Problem

Don't stop reading when you see the word math - because this is really cool and you'll miss it. (Besides, you can make MONEY on it if anyone is willing to take the bet!)

There is an interesting problem in math: How many people do you need to gather before you get to the point where there is a 50% chance that two people in the group share a birthday?

Make a quick guess before reading on.

It may surprise you to find out that if you have a group of only twenty-three people you have a slightly better than 50% probability that 2 of them share a birthday. If there are 30 or more people in the room the odds are overwhelmingly in your favor if you bet that two share a birthday. Most people have a hard time believing this, so you should be able to find someone to bet against you.

(The "twist" is that you can't specify the date. It's just any two people sharing A birthday. If you specify the date, the probability drops astronomically. So if you want to win the bet, don't say, "I bet 2 people in this room have a birthday on April 20." You will lose unless you know twins who are there with that birthdate!)

SO, what are the chances that I personally know MORE than two people that have today,the SPECIFIC date March 2, as their birthday?

While you ponder that, let me send out birthday greetings to the March 2 birthday people I know:

Uncle David
Michelle V.
Michelle V.'s mom
Kevin E.
Florence M.
Florence M.'s grandson
John F
My cousins' grandma on the other side

HAPPY BIRTHDAY to all of you!!!

And especially to Mom on a milestone!

Since it's not proper to share a woman's age, I won't say which. :-)

It must be that March 2 is a really good day to be born!

Can any of my readers beat my record of personally knowing 9 people with birthdays on the same day? You can't include celebrities or others outside your circle of friends and family - and no fair including multiple births.


Anonymous said...

Heidi: I would like to add another to your March 2 list. Debbie's daughter will celebrate her 27th today. Dad

Heidi said...

I guess I need to add to my list - also just noticed in the Immanuel newsletter at Grandpa's today that Bea O. also has a birthday on March 2, so that brings the list to 11 for both of us since we know the same people!