生日相同的機率

The probability of my birthday is 29thFeb = Pa = 1/ (365x4 +1) = 1/1461
The probability of my birthday is not 29thFeb = Pb = 365x4/ (365x4 +1) = 1460/1461
The probability that no one (of n-1 people) same as mine, Pc
= Pb x {(1460 -4)/1461 }^(n-1) + Pa x (Pb)^(n-1)
=1460 x{ (1456)^(n-1) + (1460)^(n-1) } /(1461)^n

Hence, the probability of at least 2 people has the same birthday =1-Pc

2006-12-11 20:26:53 補充：
SORRY" Hence, the probability of at least 2 people has the same birthday =1- n x Pc "

2006-12-12 23:50:13 補充：
OIC !! 某人. Thank you very much. I have learned a lot from you. But, I still wonder why the analysis did not include 29th Feb ????

2006-12-19 00:53:34 補充：
Actually, I made a mistake and did not make a complete analysis. I have already surrounded to 某人... it is very lucky to get 40 points.

哩個係數學上有名o既"Birthday Paradox"

N 人, 最少有兩人生日相同的機率
P(n) = 365!/[(365^n)(365-b)!]

經過Approximation,
P(n) = 1 - e^[(-n^2)/(2.365)]