[Math] Matching Birthdays...

Imagine · May 20, 2012

Alright, so this is the situation:

You are having a party with many guests, and your guests are arriving one by one. Assuming an equal distribution of birthdays (That is, each day of the year is equally likely to be a birthday), and equal distribution of whatever else (no twins, etc), after how many people entering the room will the probability that any two of them share a birthday be at least 50%?

tl;dr : How many people are required to be in a room so that the probability that any two of them share a birthday is at least 50%?

If you have the answer (And you got it yourself- no cheating with google), post it here. (No solution unless multiple people have posted

)

thatguy1234 · May 20, 2012

23 should be the answer cause im smart like that

Imagine · May 20, 2012

Or because you used google

Noam · May 20, 2012

I'm going to say that it needs to be half the value of one year + one day, so half of 366 but I'm going to scrap up a python script to text my idea later
183

SuF · May 20, 2012

I knew it was a low number because you have to add the probabilities of everyone matching with everyone else and that gets rather large rather fast.

Jack · May 21, 2012

Awkward.

I saw this question and knew it was 23 as my math teacher actually told us this 2 weeks ago haha.

Atleast I was able to crack this math question, doubt I'll manage any of the others.

MMA · May 21, 2012

Isn't it like 10 or 20? Heard this some where b4 but can't remember.

Apith · May 21, 2012

SuF said:
I knew it was a low number because you have to add the probabilities of everyone matching with everyone else and that gets rather large rather fast.

Same. I knew it couldn't have been one of those simple questions, and there was something behind it. I cba to do the math so I just read through and found the answer. You need to lose common sense for this, or you'll end up with 183.