Question 1103160: How many people would you have to have in a group so that there is a probability of at least 0.9 that at least two of them will have the same birthday?
Answer by Boreal(15235)   (Show Source):
You can put this solution on YOUR website! Can do this on a spreadsheet where
p(2) not is (364/365)
P(3) not is (364/365)(363/365)
p(22) not (1/365)^21*(364*363*...*341)
Here, when not is less than 10% the probability of yes will be greater than or equal to 90%.
n=41
On a calculator, can do 365*364*363*... to about 345, then divide by 365^21. That will keep it from overloading. Then repeat, and when 326 changes to 325, it will be <10% or >=90%.
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