Want a Free Job Posting?

Buy a job posting today and the second one is on us. For a limited time only. Act Now.

Interview Question

Interview Chicago, IL

What is the chance that at least two people were born on

  the same day of the week if there are 3 people in the room?

Interview Answer

5 Answers



Anonymous on Nov 22, 2010

incorrect. 1-364/365*363/365 = 1-.9918 = .0082...something like this for 2 people, for 2+ add in the chance of 3 of 3. So first guy then gets 365/365 choices, next two get 1/365

Chase Schwalbach on Jan 18, 2011

Also incorrect... They are asking if they were born the same day of the week not the exact same day as Chase alluded to. In this case the easiest way to do the problem is 1- probability that no one was born on the same day. 1-(1)(6/7)(5/7)+ 19/49 or 38.78%

traderguy on Jan 22, 2011

My bad =19/49

trader guy on Jan 22, 2011

Or you can calculate it directly: The chance of SELECTED two people(but not three) that are born on the same day is 1* 1/7 - 1/7*1/7 =6/49 Now we have 3 chooses 2 = 3 possible pairs, so the probability that any PAIR(but not all three) that are born on the same day is 3* 6/49 = 18/49. However, since the question asks "at least 2", we will need to add the possibility that all three are born at the same day, which is 1/7 * 1/7 = 1/49. So the final result is 18/49 + 1/49 = 19/49 This obviously is a worse way of calculating it, but it's an alternative for some people who wants to think "straight".

K Z on Mar 26, 2011

Add Answers or Comments

To comment on this, Sign In or Sign Up.