How many people in a room?

For 2023 (and 2024 ...) - we are now fully retired from IT training.
We have made many, many friends over 25 years of teaching about Python, Tcl, Perl, PHP, Lua, Java, C and C++ - and MySQL, Linux and Solaris/SunOS too. Our training notes are now very much out of date, but due to upward compatability most of our examples remain operational and even relevant ad you are welcome to make us if them "as seen" and at your own risk.

Lisa and I (Graham) now live in what was our training centre in Melksham - happy to meet with former delegates here - but do check ahead before coming round. We are far from inactive - rather, enjoying the times that we are retired but still healthy enough in mind and body to be active!

I am also active in many other area and still look after a lot of web sites - you can find an index ((here))

How many people do you need to gather in a room for there to be an even chance that two of them have the same birthday? Would you believe that it's as few as 23? This is something I've heard said over the years but I wasn't sure if I believed it. Well - here you go:

Day 18, chance is 35.5%
Day 19, chance is 38.9%
Day 20, chance is 42.2%
Day 21, chance is 45.6%
Day 22, chance is 48.9%
Day 23, chance is 52.1%
Day 24, chance is 55.4%
Day 25, chance is 58.5%

Sure ... I used Perl ;-)

#!/usr/bin/perl
$chance = 0;
for ($k=1; $k<25; $k++) {
$chance += ($k/(366 - $k)) * (1 - $chance);
printf "Day %2d, chance is %5.1f%%\n",$k+1,$chance*100;
}

Yes - I DID do a test / sanity check. Ran it up to 365 people and ended up at 100%
(written 2004-08-12, updated 2012-11-04)

Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles

P207 - Perl - File Handling
  [114] Relative or absolute milkman - (2004-11-10)
  [255] STDIN, STDOUT, STDERR and DATA - Perl file handles - (2005-03-23)
  [616] printf - a flawed but useful function - (2006-02-22)
  [618] Perl - its up to YOU to check your file opened - (2006-02-23)
  [702] Iterators - expressions tha change each time you call them - (2006-04-27)
  [867] Being sure to be positive in Perl - (2006-09-15)
  [1312] Some one line Perl tips and techniques - (2007-08-21)
  [1416] Good, steady, simple example - Perl file handling - (2007-10-30)
  [1442] Reading a file multiple times - file pointers - (2007-11-23)
  [1467] stdout v stderr (Tcl, Perl, Shell) - (2007-12-10)
  [1709] There is more that one way - Perl - (2008-07-14)
  [1841] Formatting with a leading + / Lua and Perl - (2008-10-15)
  [1860] Seven new intermediate Perl examples - (2008-10-30)
  [1861] Reactive (dynamic) formatting in Perl - (2008-10-31)
  [2233] Transforming data in Perl using lists of lists and hashes of hashes - (2009-06-12)
  [2405] But I am reading from a file - no need to prompt (Perl) - (2009-09-14)
  [2818] File open and read in Perl - modernisation - (2010-06-19)
  [2821] Chancellor George Osborne inspires Perl Program - (2010-06-22)
  [2833] Fresh Perl Teaching Examples - part 2 of 3 - (2010-06-27)
  [3326] Finding your big files in Perl - design considerations beyond the course environment - (2011-06-14)
  [3548] Dark mornings, dog update, and Python and Lua courses before Christmas - (2011-12-10)
  [3830] Traversing a directory in Perl - (2012-08-08)
  [3839] Spraying data from one incoming to series of outgoing files in Perl - (2012-08-15)

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Some other Articles

Python training
90 to 10 or 80 to 20 rule
London - Most expensive city??
Mobile Office revamp
How many people in a room?
A bolt of lightning on Multicasting
What do you look for in your IT trainer?
Study room - the Oxford train
How much does fuel cost for an airline flight?
Writing on a Sunday

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This is a page archived from The Horse's Mouth at http://www.wellho.net/horse/ - the diary and writings of Graham Ellis. Every attempt was made to provide current information at the time the page was written, but things do move forward in our business - new software releases, price changes, new techniques. Please check back via our main site for current courses, prices, versions, etc - any mention of a price in "The Horse's Mouth" cannot be taken as an offer to supply at that price.

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