[ANNOUNCE] London Perl Mongers Technical Meeting 12th April 2010

Uri Guttman uri at StemSystems.com
Sat Mar 27 20:49:14 GMT 2010

>>>>> "CJ" == Christopher Jones <c.jones at ucl.ac.uk> writes:

  CJ> On 27 Mar 2010, at 18:16, Dave Cross <dave at dave.org.uk> wrote:

  >> On 03/27/2010 09:10 AM, Luis Motta Campos wrote:
  >>> Dave Cross wrote:
  >>>> On 03/27/2010 08:13 AM, Uri Guttman wrote:
  >>>>> and paul and i share the same birthday. not sure what that means.
  >>>> I expect you'll find it's a coincidence :-)
  >>> As a mathematician I must say coincidences have really low
  >>> probability
  >>> of happening...
  >> Given the number of people who have birthdays and the relatively
  >> small number of days available to have them on - you might want to
  >> recheck your working there :)

  CJ> According to someone cleverer than me, you need a group of only 57
  CJ> people to have a 99% chance that two of them will share a birthday....
  CJ> This odd result of probability is called the "Birthday Paradox";

  CJ> http://en.m.wikipedia.org/wiki/Birthday_problem?wasRedirected=true

and only about 20 (i think 21.x) people for a 50% chance. that is a
better party bet as few (other than geeks) would know the true odds of

and it isn't an odd result, it is very simple probability odds. and the
trick is not to calculate the odds of duplicate birthdays but the odds
of no duplicates and subtracting from one. 364/365 * 363/365 ...

did this one in high school (decades ago) on an old calculator.


Uri Guttman  ------  uri at stemsystems.com  --------  http://www.sysarch.com --
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