You can also use List::Util to get the sum, and then divide by the number of elements using scalar @array.

#!/usr/bin/perl

use strict;
use warnings;
use List::Util qw( sum );

my @box = ( 100, 200, 300 );
my $average = (@box) ? (sum (@box) / scalar @box) : 0 ;
print $average, "\n";
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neniro

Oh, i missed Art_XIVs node, suggesting the same.