I think the question is usually frames as “how many people does it take to make it at least 50% likely that two people will share a birthday”, or more likely than not etc.
A guarantee would need 366 people. But most people are satisfied with “more likely than not”, “90% chance”, or “99% chance”.
366 would not guarantee it. That’s not how probability works. You cannot guarantee a shared birthday without selecting people. And not to mention, birthdays aren’t evenly distributed.
I misunderstood the scenario. For some reason I was thinking that if you randomly selected people and had a duplicate birthday that’s what you didn’t want.
If you assume one mass shooting every three days for the last 15 years, and there being 1700 people “present” for each (within earshot, not necessarily immediately in danger), there are now over 3 million people who have now been present for shootings.
There’s a similar and related math problem for this:
How many people do you need in a room before 2 of them share a birthday?
The answer is around 50, which is way less than most people expect.
At 50 people is is 97% likely and at 60 people it is 99% likely.
So not guaranteed, but surprising if nobody shares a birthday.
https://en.wikipedia.org/wiki/Birthday_problem
The math on it really defies most people’s intuition
I think the question is usually frames as “how many people does it take to make it at least 50% likely that two people will share a birthday”, or more likely than not etc.
A guarantee would need 366 people. But most people are satisfied with “more likely than not”, “90% chance”, or “99% chance”.
EDIT: I meant 367, not 366!
More than 50% is like 20 people.
It would take 367 for a guarantee because of leap years.
366 would not guarantee it. That’s not how probability works. You cannot guarantee a shared birthday without selecting people. And not to mention, birthdays aren’t evenly distributed.
Once you have more people than days in a year it’s not about statistics anymore
366 people wouldnt guarantee no shared birthdays though. There could still be one leap year baby in that bunch. But what are the odds in that?
2.6 • 10^-158 , if anyone is curious.
That sad experiment where 366 people in a room all have the exact same birthday.
Statisticly unlikely, but definitely possible.
I misunderstood the scenario. For some reason I was thinking that if you randomly selected people and had a duplicate birthday that’s what you didn’t want.
i also interpreted this how you did. you are not alone, internet stranger
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Oops – I meant 367!
If you assume one mass shooting every three days for the last 15 years, and there being 1700 people “present” for each (within earshot, not necessarily immediately in danger), there are now over 3 million people who have now been present for shootings.