00:01
So in this question, we want to work out the probability that two people in a room of 11 share the same birthday.
00:07
So first of all, what's the probability that all 11 people have different birthdays? so probability 11 different birthdays.
00:21
Let's call that p.
00:23
So p is going to be, so for the first person, they can be born on any day of the year, 365 over 365.
00:31
For the second person, they can't be born on the same day as the first person.
00:35
So there's a 364 over 365 chance.
00:40
For the third person, they can't be born on any of the same two days as the first ones.
00:45
So we've got 363 over 365.
00:48
And we're going to go all the way down to 365 minus 10 is 355 over 365.
01:00
So what's this? well, it's 365 factorial, divided by 365 to the power of 11, times...