The Birthday Paradox
Heard this on the radio recently ... How many people do you need in a room to have a 50% chance of two having the same birthday?
https://betterexplained.com/articles...thdayparadox/ 
Haven't opened the link but IIRC it's about 2530. Then at about a 95% chance it's around 40
Of course to have a 100% chance you need at least 367 people  one for each day of the year plus one more. 
Opened the link  a couple fewer than I thought. and 95% was 48.
Really cool piece of stats. Frequently used by Maths teachers to impress their classes. 
Has anyone actually tested this out for real?
I get the logic but still struggle to see that if in reality if you grouped together a number of times 23 people that reality will match the logic used. 
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I actually like the Monty Hall Problem. But it tends to be more relevant to Americans that have watched Let's Make a Deal. 
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Report back tomorrow :) 
I was on a train with 10 friends on a day out, and not one of us had the same birth month, which i thought was kind of freaky.

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I know a lot of BBS Members don't advertise their birthday, but out of 6,944 members I would think at least 25% would. (Just look at this thread for example).
That would be a data base of 1,736 known birthdays. Divide that by the magic 23 and you get 75 subsets. My fuzzy logic is that would mean at least 150 BBS members would have a birthday today (a minimum of 2 per 23 subset), yet the forums page shows there are only 5. Stick that in your pipe and smoke it! 
I worked in an office of 9 people before and 3 of us shared the same birthday.
About 20 years apart in age but unusual nonetheless. 
Hedgehog, you should never get a job in statistics.

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Very true! :) 
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Edit  beaten to it ! 
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The original problem was any two the same, not someone else the same as you which is a) very different and b) the way we intuit the (wrong) answer. 
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Remember reading this at the time, World Cup squads are perfect as there are 23 players in each one, in the 2014 the number of teams with 2 or more players with the same birthday was indeed 50%, I'm the same as you I just can't believe it would actually work out but seemingly it does
Here is the article and the proof www.bbc.com/news/magazine27835311 Quote:

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Since I didn't see an article related to the birthday stats of this year's World Cup squads, I did it myself. Of the 32 teams, 16 have two players with the same birthday. Poland takes the title with 4 sets of players with the same birthday. (all different ages, though) Portugal has three sets of players and Morocco and Brazil have two sets of players with the same birthday.

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