Math question:30 people are at a party... Am I right?

[Gaidin]

2) Well, maybe you should diversify more? Using that formula on this problem would be VERY time consuming.

Ever try to explain something from the standpoint of a context you're not familiar with? It's not pretty. Especially when trying to figure out a proper probability equation. Those things are easy to screw up.

[Nikitn]

probability is easy to screw up, I can agree with that

[Gaidin]

probability is easy to screw up, I can agree with that

As an aside i figured out why I said 22 instead of 23. With my stance of taking the probability that they don't match it takes 22 to hit the probability just before 50%. Which means you need one more to break 50 on them matching. Funny error-that-isn't-an-error.

[Nikitn]

P(none of the 22 people's birthdays match)= 0.493 according to you, while that is not correct, it is too low. The correct answer would be P(none of the 23 people's birthdays match=0.493

Either that or I don't understand you.

[Gaidin]

P(none of the 22 people's birthdays match)= 0.493 according to you, while that is not correct, it is too low. The correct answer would be P(none of the 23 people's birthdays match=0.493

Either that or I don't understand you.

My problem is for 22 extra people. The problem of a single person is trivial. A quirk in the wording, nothing more.

[Nikitn]

Yes, that was what I said all along. I never claimed your model to be wrong

Gaidin; when n=22 there are actually 23 people who have been selected. An example: 2 persons would be (365/365)(364/365)=1*(364/365)=364/365=P(2 randoms not having their birthdays on the same day). So, even if n=1 in this case, 2 people have been questioned. Just like when n=365, the probability is 0 because 366 people have been questioned.

[Fight!]

I started performing a Chi-Sq test out of disbelief (I had figured it would be much lower and could not remember the formula for the problem) but after I saw how many people I knew had the same birthday, I figured it wasn't necessary