What day is your birthday?

[sdave]

This group has beaten the typical odds. 30 birthdays with no matches. Only a 30.3% chance of that happening. But, you'll also notice how close several of the birthdays are. Ones on Aug 28, 29th, and 30th. Ones on Sep 20th & 21st. Ones on November 5th & 6th. And finally, birthdays on December 17th and 18th.

This is often referred to as the birthday paradox. It's not intuitive. Most people are looking at the odds of sharing their birthday with the other 22 people. The odds of any two random people sharing their birthday is 1/365 (not counting for leap year). Extremely low. However, you need to look at all of the permutations, not simply comparing your bday with everyone else. 23 people gives you 253 possible combinations. You calculate it by figuring you have 22 possible matches, the next person has 21 because your birthday has already been factored in, the next person has 20 possible matches... all the way down to the final two people (22+21+20+19... +1). Another way to compute this is n * (n-1) / 2. So, it would be 23 (22) / 2 = 253).

The odds of two people not having the same birthday is 99.726027% (364/365)

-If you have 23 people, you have 253 working combinations. Meaning, you need to multiple .99726027 by itself 253 times. So...

.99726027 ^ 253 = 0.49952234 (the odds of not having a birthday match)

1 - .49952234 = .50047777 (odds of having a birthday match)

Technically, 50.048% of finding a birthday match with 23 people. You would be right roughly 50% of the time.

-With 30 people, there are 435 birthday combinations (30 * 29)/ 2 )

.99726027 ^ 435 = .30318317

1- .30318317 = .69681683

69.68% of having a birthday match with 30 people.

If we get to 40 people, the odds will increase to 88.2%. So yes, get 10 more people, and the odds are going way, way, up.

there was someone else whom said they had a 13 Dec birthday, so that’s at least two.

 

[csregor]

One thing I remember from stats class, is if there are 23 people in a room, the odds of having at least one birthday match is 50%. Odds increase to 70% with 30 people. Just curious to see if we can find at least one match. No reason to lie. You don't need to post what year you were born, obviously.

Mine is May 28th.

10/29

 

[cdbearde]

It figures you're the only one that would figure that out. I suppose that is why I Like you. Nah, really 19th.

🤣 Is that why you told me you were beautiful? I am still waiting for the picture.
Della, this is good humor, but you need to post a pic. 👍RollLaugh
It's like stand up or stand down. 🤣 🤣

 

[dukedevilz]

there was someone else whom said they had a 13 Dec birthday, so that’s at least two.

Nice! We're up to 3 separate matches. Forever birthday buddies:

May 15- @RR30 @boilerzz
July 3- @WeAreDePaul & @IUfanBorden
Dec 13- @Jaycg15 & @sdave

 

[dukedevilz]

For real? You celebrate on March 1 most years?

It figures you're the only one that would figure that out. I suppose that is why I Like you. Nah, really 19th.

I always thought it was funny how they would say Chucky Brown was 6-7 years old when he played in the league.

Here's a fun little fact about Leap Year. I'm sure some of you are already aware of this. It's not actually every 4 years, as we're often told as kids. Yes, every Leap Year has to be divisible by 4. But, when you come to the close of a century, it also has to be divisible by 400. Meaning, 2000 is a leap year. But, the years 2100, 2200, and 2300 are not. It takes Earth 365.242189 days to revolve around the Sun. Obviously we would be off, every so slightly, if we had it every century, as the number isn't quite 365.25. Taking away Leap Year three times every 400 years helps our calendars stay in alignment with the natural course of the Earth.

 

[CB3UK]

9/6. John Wall commited to UK specifically because we share the same bday. You're all welcome.

 

[sgrooms]

December 14th

 

[sdave]

December 14th

have you always been one day off?

 

[wesr]

November 23rd

my wife’s bday