How many people to be invited to party in order to make it likely that
there are three people with the same birthday?

Hello.

You'd need to invite 88 people to the birthday party according to the
solution to Question #2 on a web page called "Coincident Birthdays"
hosted by Mathcad.com:
http://www.mathcad.com/library/LibraryContent/puzzles/soln28/soln28.html

The complete solution is on that web page.

For 87 people, the probability that 3 had the same birthday would be
0.499455.
For 88 people, the probability that 3 had the same birthday would be
0.511065.

Thus, in a group of 88, it is more likely than not (>.50 probability)
that 3 will have the same birthday.

Additional source:
"Among other things, the minimum number of people to be gathered
together so that at least three would have the same birthday with the
probability higher than 1/2, is 88."
http://www.cut-the-knot.org/do_you_know/coincidence.shtml


search strategy:
"how many people" "have the same birthday"

I hope this helps.

---

Clarification of Answer by juggler-ga on 01 Oct 2003 23:11 PDT

Correction:
"... 88 people to the party..."
(The party isn't necessarily a "birthday party." Sorry for that typo.)