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Monday, June 16, 2008

What are the Odds?

At lunch today, I had a funny experience that I just had to share. The person I met for lunch (a CEO at a client company) today is his birthday. And, it's my birthday. And it's today.

So, if I'm right, then it's a 1 in 365.25 chance that we share a birthday. And maybe a 20 in 365.25 chance that it would be on our birthdays that we get together. So, that's roughly a:

1 in 6,700 chance

and even the chance of that happening in a lifetime is pretty remote.

It just struck me as a pretty cool occurrence.

The only disappointing part is that when we told the waitress that it was both our birthdays, she seemed completely unimpressed. (But she did give us each free dessert.)

18 comments:

Sue Waters said...

Happy Birthday for yesterday since it is now today here. And it was a pretty cool occurrence.

Blogger In Middle-earth said...

Tēnā koe Tony

And many Happy Returns of the day (backdated of course)!

On my way to work this morning I spotted a car with the registration number AJ6837! What a coincidence that was. What do think the chances of me spotting that one would be? Pretty small I'd say :-)

Ka kite
from Middle-earth

Tony Hirst said...

If there were more than 23 people in the place you were eating, the odds were greater than a half that two people in the room would share a birthday... so why not you two?!

homo sapiens v. 2.00 said...

Well, that means that everyday there are at least 1 million of people who meet each other in their same birthday.

Happy birthday.

Karyn Romeis said...

Belated birthday greetings. I had a few thoughts about your waitress.

(a) Perhaps she thought you guys routinely meet up on your birthday and didn't appreciate the measure of the coincidence
(b) She meets people who are having their birthdays every day in her job. She probably also meets a lot of people who say it's their birthday so that they can get a free dessert.

I once went out on a blind date and discovered that the date and I shared a birthday. We were an item for a few months, but his mother didn't approve of me, so... :o(

Tony Karrer said...

Ken - yes it was random, but not as random as that.

Tony - I believe it's 25 people, and that's greater than 50% odds, but we were also sitting at the same table AND on our birthday. I did think about the 25 people in a room thing which always seemed low, but this is MUCH longer odds.

HSv2 - Yep, there's a million people that it happens to, but a bunch more that it doesn't.

Wow, this crowd is tougher than the waitress. :)

Karyn - that's probably it on the waitress. Since I go to the same restaurant, I'll have to ask her the next time. :)

hugh.greenway said...

Well Happy Birthday not only have you got me reading blogs, you've got me commenting. I always thought it was 23 and here's the maths http://www.pluralsight.com/wiki/default.aspx/Craig/BirthdayProblemCalculator.html

Just to add to the fun, two of my staff shared your birthday yesterday and they were born in the same year as each other. I have only 200 staff.
Hugh Greenway

Malinka said...

Tony, Happy Birthday! And thank you for interesting and useful posts!

Tony Karrer said...

Hugh - it's great to see your comment. I hope you started from an RSS reader, right?

Okay, I'll go with 23. And two of Hugh's staffers shared my birthday. Boy, I thought this seemed so cool.

Sue - thanks for saying "it was a pretty cool occurrence" ... luckily my wife thought so last night when I shared it with her. Or maybe she was humoring me because it was my birthday. :)

V Yonkers said...

I had a coworker who shared a birthday. Not only did we both have red hair (I don't know the odds, but I know it is high), but we both showed up to work on my first day on crutches (same injured leg).

Happy belated birthday.

Mark Frank said...

I am with the waitress.

I can see it is an interesting coincidence that when you had lunch with someone on your birthday it turned out to be their birthday as well - but that's only 1 in 365. The fact that you only have lunch with that particular person 20 days a year is irrelevant. To take an extreme case - suppose you never have lunch with the same person twice - the chances that when you had lunch with someone on your birthday it turned out to be their birthday as well would still be 1 in 365.

Tony Karrer said...

Dang you Mark. You are right - it's a 1 in 365.25 chance that my lunch person has my birthday. So, if I go to a business lunch on my birthday about 30 times in my life, then there's about an 8% chance that I'll eventually have lunch with someone who shares my birthday.

Now that doesn't seem so great.

Don't get me wrong, I still think it was a neat occurrence - but maybe not quite extraordinary enough to warrant a blog post.

Especially one that makes me realize my once proud skills in probability have left the building.

Tony Karrer said...

Oh, Mark, the reason for the 20 in the original post is that was my estimate for the number of lunches I would ever have on my birthday. But I've decided to live longer and have more lunches on my birthday to see if it happens again to me.

Steptimer said...

Happy Belated Birthday Tony! Thanks for sharing a very useful posts!

Hope to see few more in futures.. Thumbs up keep on posting..

deepikaur said...

That's pretty insane! I wonder how often that happens: two people with the same birthday meet on their birthdays, without knowing it was each other's birthday. I've never met anyone (face to face) that shares my birthday, sadly.
Happy late birthday to the two of you!

Tyron said...

Happy Belated Birthday Tony!! and thanks for the continued reeducation of Tyron when it comes to blogs and e-learning.

Laura Kratochvil said...

Okay, now what if you were the same age? Even close?

Tony Karrer said...

Laura - we were 5 years apart. Scary that he was 5 years younger than me. :)