What is the probability that at least 2 students in a class of 36 have the same birthday?

Given a group of n students, and given the fact that there are 365 days in one year, the probability that there are no students with the same birthday is given by

Therefore, the probabilty that there are at least 2 students with same birthday is the complementary of this value:


And if we use n=36 (number of students), we find

So, the probability that there are at least 2 students in a group of 36 with same birthday is approximately 83%.

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