Re: Re: Birthday Chances

[thraxil]

you're close on the math.

(ignoring leap-years) the probability that n people all have different birthdays is: ((365-1)/365) * ((365-2)/365) * ((365-3)/365) * . . . * ((365-n+1)/365) = 365! / ((365-n)! * 365^n)

setting that equal to 50% and solving is probably harder than just plugging in numbers on a calculator till you get it. 23 is the magic number.

anders pearson

[ckohl1]

To expand on what thraxil has said...

This probability and permutations exercise could be written as:

#!/usr/bin/perl -w
use strict;

my $DAYS_IN_YEAR = 365;

print "\n# of People \t Birthday Match Likelihood\n" . '-'x80 . "\n";

for my $people ( 2 .. 40 ){
    my $tmp_days = $DAYS_IN_YEAR;
    my $probability=1;
    for ( 1 .. $people ){
        $probability *= $tmp_days--;
    }
    $probability /= $DAYS_IN_YEAR ** $people;
    $probability = ( 1 - $probability ) * 100;
    print "$people \t\t $probability %\n";
}

exit;



Chris