Question 697673: what is the probability that two people selected at random have the same birthday? ignore leap years.
Answer by Positive_EV(69)   (Show Source):
You can put this solution on YOUR website! There's two possible ways to look at this problem:
1) The birthday of the first person actually does not matter. You only care if the second person's birthday is the same as the first. Thus, the probability that the second person's birthday matches the first is the probability that a specific date is selected as one person's birthday, which is 1/365 ignoring leap years. Basically, select any date; that becomes the first person's birthday, and the probability that the second birthday matches is 1/365.
2) There are 365*365 possible combinations of birthdays for the pair of people. Of these possible combinations, there's 365 combinations where the birthdays match (both January 1, both January 2, etc.). The probability is the number of combinations of matching birthdays over the total number of combinations of birthdays, which is (365/(365*365)) = 1/365.
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