When is your birthday?

[Bub]

This video says that the odds are about 50:50 that 1 in 23 people will have the same birthday.
http://www.wimp.com/justcoincidence/
Mine is August 22
8/22

 

[Doc Manhattan]

Love it!

(I'm a math nerd at heart... even if my grades were never very good in the subject.)

 

[Bub]

Does anyone want to see if these numbers are correct by listing your birthday?

 

[CLRV]

3/24/84

 

[SmokeyTweed]

3/17/83

 

[Cody V]

07/06/86

 

[Bub]

Thanks, we just need the month and day

 

[Frost]

7/1

 

[mark]

7/8

 

[Milan]

12/13

 

[Doc Manhattan]

Does anyone want to see if these numbers are correct by listing your birthday?

As the video says, there's no meaning in testing an assertion about absolute probability; it's just true. (Not to be confused with sports book odds, which are really just educated guesses.)

We have more than 366 members here, so the probability of duplicate birthdays on the board is 100%. If we had 1 member, the chance would be 0%. The odds can be figured out absolutely for every number in between those limits.

The odds of 2 members out of any 22 picked at random sharing a birthday is ~50% That means that the odds are just as good that we wouldn't see a match, but it doesn't change the odds.

Whether we saw a match or not, the 50-50 odds would be demonstrated equally. When you toss a coin and it comes up heads, that doesn't mean that the tails side stops existing or coming up on half of any other tosses.

 

[CLRV]

My brain hurts now Doc.


:lol:

 

[Doc Manhattan]

My brain hurts now Doc.


:lol:

I should just stick to teaching English!

 

[Ataki]

3/13

 

[Bub]

Doc said

We have more than 366 members here, so the probability of duplicate birthdays on the board is 100%. If we had 1 member, the chance would be 0%. The odds can be figured out absolutely for every number in between those limits.

I am just curious how long it takes to find two people who have the same birthday.
Initially I thought that it would be a much larger number.
Doc, if you teach 5 classes with 30 people how many classes would have 2 people with the same birthday?

 

[LIPIPE]

Bronx Bill and I (Bronx Marty) have the same birthday born one year apart in the same NYC borough, home of the New York Yankees...May 13th

 

[Bub]

so far 9 birthdays and no matches

 

[Doc Manhattan]

Doc, if you teach 5 classes with 30 people how many classes would have 2 people with the same birthday?

Probability says the odds of a duplicate in each class are independent. With 30 people, the odds are good (about 57%) I'll have duplicate birthday in that class, but whether I do or don't doesn't affect those same odds in either class, the same way a die rolling 6 doesn't affect a separate die from rolling any number.

But I can extrapolate the odds of any possible combination of duplicates by multiplying the independent odds, which say the odds are on 3 matches, 2 no-matches, but they're very narrow odds... I wouldn't bet $5 on it, to put it that way.

 

[RealtorFrank]

3/16

 

[Bub]

Doc, I agree, but can you ask them?
They might find the results surprising.
I still find it hard to believe that in a classroom the odds are 50:50 to find 2 people with the same birthday.