my $sum  = 0;
       $sum += $_ for @total;

    my $average = $sum / @total;


##</code><code>##


    my $average = 0;
       $average = ($_ * $average + $total[$_]) / ($_ + 1) for 0 .. @total -1;


##</code><code>##

    perl -lane '$a = (($. -1) * $a + $F[2])/$.; END{print $a}' file
    


##</code><code>##


    perl -lpe '$,+=$_}{$_=$,/$.' file