The formula to get the total number of all possible combinations can be found at Wikipedia if you do not remember it. Then just increase a counter for each combination and print the ratio:

#!/usr/bin/perl
use warnings;
use strict;

use Algorithm::Combinatorics qw(combinations);

my $rep  = 10;
my @data = 1 .. $rep;
my $size = 4;
my $iter = combinations(\@data, $size);

my $maxcount = 1;
$maxcount *= $_ for 1 + $rep - $size .. $rep;
$maxcount /= $_ for 2 .. $size;

my $count = 1;
while (my ($w, $x, $y, $z) = @{ $iter->next // [] }) {
    $count++;
    next unless $w-2*$x+$y or $x-2*$y+$z;
    print $count/$maxcount, "\t$w, $x, $y, $z\n";
}
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