my $h = { 
        a => 0.1,
        b => 0.5,
        c => 0.4,
};

for (1..10000)
{
        $s{rand_key($h)}++;
}

print "output: ".join(" ", %s),"\n";

sub rand_key {
        my $h = shift;
        my $r = rand();
        for (keys %$h)
        {
                $r-=$h->{$_};
                return $_ if($r < 0); 
        }
        return undef;
}
__END__
output: c 4024 a 1017 b 4959