Birthday Room

While we are on the subject of probability and the tendency to ascribe supernatural causes to events, I thought I’d pose another problem for everyone.

You go to a party and there are seventy people there, none of whom you know personally. You get into a conversation with someone and find out that the person has the exact same birthday as you! You are completely shocked and think that some supernatural power has placed you in this position. You also think that the two of you were destined to meet.

So the question I have for you is: What is the probability that 2 people in a group of 70 have the same birthday?

This time the person who gives me the correct answer gets a Gmail invitation, not that they are worth anything now.

Oh and please resist from googling the answer. Well you could, but then it wouldn’t be as much of a fun exercise for you, would it?

Comments (3)

  1. Niket wrote::

    1 - [365 C 295]/(365^70)

    Thursday, August 26, 2004 at 12:47 pm #
  2. Niket wrote::

    The above answer is same as
    1 - [365 C 70]/(365^70)
    and it is wrong. :(
    I know the right answer now… but I realized the mistake after googling for it. So, let me not spoil the fun anymore.

    Thursday, August 26, 2004 at 12:54 pm #
  3. There fails the law of probability when u believe in destiny and the supernatural power.
    Though i m a non-believer in god, i do believe in the destiny playing a kinda role in every body’s lives.
    any takers??
    ….sateesh k.

    Friday, August 27, 2004 at 12:25 pm #

Trackbacks/Pingbacks (2)

  1. kaisare.net » An exercise in Probability and destiny on Thursday, August 26, 2004 at 3:13 pm

    [...] city is low… really low… perhaps one in several hundred thousand. But as the next post at P’s blog should indicate, that the probability of a random [...]

  2. Prashant Mullick's Weblog on Saturday, August 28, 2004 at 2:44 am

    Birthday Room Solution
    Before we get to answering the question of the Birthday Room, let us look at a simpler version of this problem.

    Consider a year that has only 5 days and consider a room full of only 3 people.

    Let us find ways in which no two people have their b…