It might be easier if you used a standard proven statistics module of which there are a number on CPAN.

For example, I have modified your code to work with the CPAN Module Statistics/Descriptive

#!/usr/local/bin/perl -w

use strict;
use Statistics::Descriptive;

open(FH, "$ARGV[0]") or die "No file specified\n";
my @temp=<FH>;
close FH;

my $stat = Statistics::Descriptive::Full->new();
$stat->add_data(\@temp);
my $mean = $stat->mean();
my $variance  = $stat->variance();
my $num  = $stat->count();

print "Number of Values = $num\n",
      "Mean             = $mean\n",
      "Variance         = $variance\n";