My point was that the chances are tiny if you consider the probabilities of being in a relationship ( being successful at it for X amount of time). My boyfriend was arguing the same point you are but the relationship part is what's making me doubtful of the validity.
It will also list all the possible name combinations if you really want to! I’ll be the first to admit I haven’t used this in class for the main reason that with 25 students in a class, the odds are a bit over 50/50 that this experiment will work.
A second reason is that the above math is over simplified to be somewhat understandable.
Suggesting it as an answer by way of the possibility that two irish twins could have the same birthday if we expand the definition to 12 months or less doesn't make it fit for what the OP is asking.
I share the same birthdate as my boyfriend, same date but also same year, our births are seperated by merely 5 hours or so.
If you had that probability, P(Same day and same year) = P(Same year) $\times$ P(Same day|same year).
But P(same day) should be roughly independent of whether you were born in the same year.
After the edit this question no longer is a dup of the linked question.
This question now asks what we can call people who were "all born on the same day of the year of any year" while that one asks about people born on the same day of the same year.
Seeing as the odds are 1/365 that any two students will match birthdays and there are 3 possible matches, it’s no surprise that two of those students share the same birthday.
(Use the combinations calculator to figure the combinations out.
Four people (lets call them ABCD) have a 1/91 chance, but there are 6 possible combinations (AB AC AD BD BC CD) so the probability becomes 1/91 6/365…and so on.