Great mystery bug (Birthday discussion) split

cfd wrote:

You'd be suprised how high the probability of something happening in a group of 22 people is.

One of my favourite facts is given a group of 23 (22 is only gonna give a % or 2 lower) people there is a 50% chance two of the people in the group will share a birthday.

Please could you explain this? I'd be very interested to see the mathematical workings out as I can't figure it out in my head!

The way to think about the problem is in the number of pairs of people.

In a group of 23 there are 23/2 * 22 = 253 pairs of people. Each pair has a 1/365 (ignoring leap years) chance of sharing a birthday. When we have 253 pairs to check it becomes likely that we'll hit a match.

(This is somewhat simplified - http://en.wikipedia.org/wiki/Birthday_problem has more detailed explanations)

Ex-DoND contestant (show #992, 23 March 2009)

Actually in my class of about 20 at primary school, I shared the same birthday with another boy. Not sure what this has to do with mystery bugs, mind.

Last edited by garylq on Tue May 05, 2009 7:13 pm, edited 1 time in total.

That's fascinating, lets do an experiment!

Everybody who reads this thread please post your birthday, lets see how many it takes before we get a matching pair.

I will start;

September 17th

* reason for edit -spelling error

14th August

Ex-DoND contestant (show #992, 23 March 2009)

December 13th

September 12th

**Joined:** Wed Feb 01, 2006 6:19 pm **Warnings:** 0

May 10th

August 4th

January 31st.

**Joined:** Fri Jul 14, 2006 6:46 pm **Warnings:** 0

14th June.

If Paul O'Grady posted here then we'd get a match as his birthday is the same date as mine.

**Joined:** Sat Jun 17, 2006 12:12 pm **Warnings:** 0

Urm there is already a birthday thread... why not use the first 22 people on there :ponder:

**Joined:** Tue Apr 21, 2009 6:25 pm **Warnings:** 0

21st June

18th April

St. Perfect ;-)

12th April. Easter Day sometimes!

4th July all Independant me :-D

12 birthdays posted so far, but still no match, please keep 'em coming!

Only another 11 to go and we will have a greater than 50% chance of a match.

Dates posted so far;

Jan 31st
Apr 12th
Apr 18th
May 10th
Jun 14th
Jun 21st
Jul 4th
Aug 4th
Aug 14th
Sep 12th
Sep 17th
Dec 13th

14th April

Hubby is a match with Aaron though on 10th May :smt023

Ex-DoND contestant (show #992, 23 March 2009)

Well we have a match with locations, as I am from Chelmsford and it seems EmmaT is too. :lol:

August 18th.

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Great mystery bug (Birthday discussion) split

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