In a group of 60 people from two match day and month of birth with a probability of 99% Bashny.Net

Birthday paradox - a statement saying that if given a group of 23 or more people, the probability that at least two of their birthdays (day and month) coincide, more than 50%.

For a group of 60 or more people the probability of coincidence of birthdays at least two of its members is over 99%, although it reaches 100% only when the group no less than 367 people (including leap years).

Such a statement may seem counterintuitive, since the probability of one born on a certain day of the year is rather small, and the probability that the two were born on a particular day - even less, but is true according to the theory of probability. Thus, it is not a paradox in strict scientific sense - the logical contradictions in it there, and the paradox is only an intuitive perception of the differences between the situation of a person and the results of a mathematical calculation.

via factroom.ru