quick question

NoQuarter

Are the chances of 2 peoples birthday falling on the same day 1 in 365??

Or is the 1 in 365 for one person and the next persons chance must be multiplied?

Danbo!

Interesting read - http://en.wikipedia.org/wiki/Birthday_problem

Michael Collins

It depends on what you're asking.

If you're asking what are the chances of the two people in question both having a birthday on some specific date, e.g. 20 April, then it's

[latex] \displaystyle \frac{1}{365} \times \frac{1}{365} [/latex]

but if you're just asking what are the chances they share the same birthday, whatever that may be, it's

[latex] \displaystyle 1 \times \frac{1}{365} [/latex]

Making all the usual disclaimers of ignoring leap years, assuming birthdays are randomn and independent etc...

It certainly gets more interesting when you consider more than two people and then the question becomes "What are the chances of at least two people sharing a birthday?" The answer shocks most people.

Michael Collins explained your question well though, if that's as far as you want to dig into it.