#### Comment Preferences

• ##### I am remembering that in grade school(14+ / 0-)

... one of the teachers tested out how if you have 30 or so people together (I forget the exact number), odds are that two will share a birthday. Twins excluded. And it worked!

It would probably work here in New Day, too, if everyone lined up their dates.

Mark Twain: It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so.

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• ##### The Birthday Problem,(15+ / 0-)

a well-known exercise in probability. I've forgotten how to compute it, but if I remember right, the probability of a match hits .50 somewhere around 25 people and at 40 it's damned near a certainty.

The free market is not the solution, the free market is the problem.

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• ##### I just fiddled with it on a spreadsheet(13+ / 0-)

If I figured it right, 50-50 comes at 19, and certainty hits 1 at 29. I might not have got it right - I forget the details of the math we got taught in class to go with - but it's definitely counter intuitive. The number's much lower than one would tend to guess.

• With 2 people, it's 1 chance of 365.
• With 3 people, it's 2 chances of 365, plus the 1 with 2 people.
• With 4 people, 3 chances of 365, plus the result for 3 people (which includes the result for 2)
• And so on.

When I added it up in the spreadsheet that way, I got the 50-50 at 19, and 1.03 at 29. If I'm right, my memory that the target number was 30 is pretty much spot on.

Excluding twins, of course.

Mark Twain: It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so.

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• ##### OK, you've sent me to the bookshelf.(11+ / 0-)

In a college level textbook it comes up in the very first chapter, the one on sampling. A probability is always a number between 0 and 1, so you can't have a value of 1.03. P(match) = .507 when r = 23, .706 when r = 30 and .891 when r = 40.
Here's the formula: Pr = 1 - N(N -1) ... (N - r + 1)/ Nr

The free market is not the solution, the free market is the problem.

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• ##### ...and on whom ever's birthday it is...(7+ / 0-)

...on October 24 DailyKos LoE and Azazello explained the statistical probability of...what the hell were they saying?...

Ignorance is bliss only for the ignorant. The rest of us must suffer the consequences. -7.38; -3.44

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• ##### dunno...was it..."Happy Birthday!" ??? :-)(6+ / 0-)

We cannot call ourselves a civilised society if we refuse to protect the weakest among us.

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• ##### In a group of 30 people(5+ / 0-)

- any random group which does NOT include twins - it is almost certain that 2 people in that group will share the same birthday. It's a probability thing.

Mark Twain: It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so.

[ Parent ]

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