When is your birthday?

Brothers of Briar

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Bub, I'll show you how it works:

With two people in the class (Mr. A and Ms. B), the odds are a little better than 1:366. Not great, but not astronomical.

Dr. C joins the class. Now the odds of a match are 3:366 = 1:122, because the total chances for a match are AB, AC, BC. Getting close to 1% odds already!

Add Mr. D, it becomes 5:366 = 1.3% odds for a match in AB, AC, AD, BC, BD, CD.

The odds are always the total combinations/366, which = the sum of the numbers from 2 to (p-1) / 366, where p = number of people in class.

At 23 people, that's 252/366 = easily more than 50%.
 
Odds are a mathematical construct...life is not.

You can go to 10,000 different classrooms with 100 students in each one and never find two people with the same birthday. Doesn't change the fact the odds were 50/50 or whatever every time. :D

If the weatherman says there is a 99% chance of rain today, but it was 70 degrees and not a cloud in the sky all day; he wasn't wrong...it's just that today decided to be in that 1%. :cheers:
 
Frost":xou6a6e1 said:
ou can go to 10,000 different classrooms with 100 students in each one and never find two people with the same birthday. Doesn't change the fact the odds were 50/50 or whatever every time. :D
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'Zactly! An unfortunately, hard probability statistics don't make people act rationally (especially when the chance of money or convenience is dangled in front of their faces.)
 
I understand the math but I would like to see the data.
So far we have 15 birthdays.
Here are the dates:
Jan (0)
Feb (0)
Mar (13,16, 17 24)
Apr (13)
May (13)
Jun (0)
Jul (1,6,8,9,29)
Aug (22)
Sep (6)
Oct (0)
Nov (1)
Dec (13)
 
Fazby":wps0ik00 said:
We have a winner!

9/6
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And you're, yes indeedy, the 22nd person to respond.

Now, do this experiment, say, 99 more times (pref. with a more random data pool) and you'll see the proof of the probability--half the groups with a match, the other half without. :shock:
 
We have two matches now boys.

9/6 and 3/24

Wonder what the odds are for two matching Bdays in one group.
 
CLRV":tzad8xpm said:
Wonder what the odds are for two matching Bdays in one group.
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That would be the square of the odds of it happening once--in this case, a little better than 1:4.
 
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