Question

there are 27 students in a class. what is the probability that at least 3 of them have their birthday in the same month ?

Answer 1

This is a lot easier than you might think. Assume that there is no month in which three (or more) students have a birthday. Then January must have two or less class birthdays, February must have two or less class birthdays, and so on.

As each month can have at most two class birthdays, there can only be 24 total birthdays in a class of 27. This is impossible and thus has probability 0.

Therefore the probability of three students in a class of 27 sharing a birthday month is 1, i.e. 100%.

Answer 2

Answer:

there is a 9times probability to 3 of them have birthday in same month