No need for recursion, here's my obfuscation: 
sub permutation {
    my ($prob, $start) = (1, shift);
    $prob *= $start-- foreach (1 .. $_[0]);
    $prob;
}

[download]
Another approach that requires thinking a bit backwards: 
sub permutation {
    my $prob = 1;
    $prob *= $_ foreach ((($_[0]+1) - $_[1]) .. $_[0]);
    return $prob;
}

[download]
Even shorter and harder on the eyes: 
sub permutation {
    my $prob = 1;
    return (map { $prob *= $_ } (($_[0] - $_[1] + 1) .. $_[0]))[-1];
}

[download]
I stand by the first I posted, though. Anyone who can get this down to a single statement gets my respect.

In reply to RE: Re: New Jersey Lottery Probability by chromatic
in thread New Jersey Lottery Probability by ergowolf

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