You are of course correct it's calculating permutations not combinations, the following sorts that out. No I'm not going to do all obfuscation stuff on it :-0

#!/usr/bin/perl -w

use strict;

my ($number, $times) = (50, 5);

print &permutation($number, $times) * 36 / ($times + 1);

sub permutation {

    my ($prob, $number, $times) = (1, @_);
    while($times) {
    $prob *= ($number - $times + 1) / $times--;
    };
    $prob;

};
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