Here is one way:

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

    my $average = $sum / @total;
[download]

And here is another:

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

Or as a one-liner (for a space delimited file with the numbers in column 3):

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

Or if the numbers are in the first column of the file:

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

--
John.