#!/usr/bin/perl

# http://perlmonks.org/?node_id=1173445

use strict;
use warnings;

use List::Util qw(sum);

my @count = (0) x 20;

for (1 .. 2e4)
  {
  my ($top, $bottom) = (20, 20 * 20);
  my @orderedRands =
    grep{  $bottom > 0 && rand(1) < $top / $bottom
      ? (--$top, --$bottom, 1)
      : (--$bottom, 0) }
    map{ ($_) x 20 } 1 .. 20 ;
  $count[$_]++ for grep {defined} @orderedRands;
  }

my $sum = sum(@count);
print "$_\t=>\t$count[$_]\t(", sprintf('%.2f', ($count[$_]/$sum)*100), "% TTL)\n" for 1 .. 20;

##</code><code>##

1       =>      20031   (5.01% TTL)
2       =>      20037   (5.01% TTL)
3       =>      19831   (4.96% TTL)
4       =>      19953   (4.99% TTL)
5       =>      19840   (4.96% TTL)
6       =>      20068   (5.02% TTL)
7       =>      19868   (4.97% TTL)
8       =>      20030   (5.01% TTL)
9       =>      19790   (4.95% TTL)
10      =>      20076   (5.02% TTL)
11      =>      19944   (4.99% TTL)
12      =>      19909   (4.98% TTL)
13      =>      20049   (5.01% TTL)
14      =>      20150   (5.04% TTL)
15      =>      19940   (4.98% TTL)
16      =>      20112   (5.03% TTL)
17      =>      19973   (4.99% TTL)
18      =>      20157   (5.04% TTL)
19      =>      20088   (5.02% TTL)
20      =>      20154   (5.04% TTL)