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Dr. Bob is Robert Hsiung, MD,
bob@dr-bob.orgShown: posts 1 to 9 of 9. This is the beginning of the thread.
Posted by JohnX2 on March 21, 2002, at 17:19:40
maybe you already heard this.30 people are in a room, what are the odds (percent chance) that at least 2 people have the same birthday?
Posted by LiLi80 on March 21, 2002, at 17:34:15
In reply to quiz, posted by JohnX2 on March 21, 2002, at 17:19:40
Posted by Phil on March 21, 2002, at 17:47:36
In reply to quiz, posted by JohnX2 on March 21, 2002, at 17:19:40
Posted by JohnX2 on March 21, 2002, at 17:56:08
In reply to quiz, posted by JohnX2 on March 21, 2002, at 17:19:40
Posted by Phil on March 21, 2002, at 18:13:05
In reply to hint: put your heads together (nm), posted by JohnX2 on March 21, 2002, at 17:56:08
Posted by JohnX2 on March 21, 2002, at 18:18:40
In reply to 70% (nm), posted by Phil on March 21, 2002, at 18:13:05
Posted by Cass on March 21, 2002, at 21:40:51
In reply to Re: 70% - Bingo! (nm) » Phil, posted by JohnX2 on March 21, 2002, at 18:18:40
Was that a math problem, or was there a trick to it? How do you calculate it?
Posted by JohnX2 on March 22, 2002, at 0:57:18
In reply to Re: 70% - Bingo! But how??, posted by Cass on March 21, 2002, at 21:40:51
> Was that a math problem, or was there a trick to it? How do you calculate it?
Some teacher quoted this to me.
I was a bit dubious.I wrote a small "C" computer program that does a brute force random simulation of the problem at hand. Basically pick a random number 1-365 and assign it to 30 variables (i.e. people). Do some cross-checking for matches. Do this a zillion times and collect the hit rate. My simulation settles at around 70.6%. I think there may be some skew from a crummy random number generator.
I also tried to figure out the formal math proof (a bit more tricky since I haven't done stats in a while). The trick is to figure out the odds of no one having the same birthday and then just subtract this answer from 100%. This gives the same answer and is much easier. My best formal proof that I came up with in the past hour gave an answer of 72%. (Although I still feel it requires more introspection, I was hoping it would correlate better with my computer run).
Sorry for the boring programming/math. I get bored. Seems I have been away from my job for too long (engineering). May be time to return to work.
Regards,
John
Posted by Cass on March 23, 2002, at 17:23:40
In reply to Re: 70% - Bingo! But how?? » Cass, posted by JohnX2 on March 22, 2002, at 0:57:18
Thanks for the thorough explanation. I take it you are in the field of mathematics.
This is the end of the thread.
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