The code you show should work. I fleshed it out to a working example(*) and it shows the correct MAX and AVERAGE for valid cell ranges. If the cell range is empty then the result will be zero/#DIV0! like the corresponding Excel formula:

    #!/usr/bin/perl

    use strict;
    use warnings;
    use Spreadsheet::WriteExcel;
    use Spreadsheet::WriteExcel::Utility;

    my $workbook  = Spreadsheet::WriteExcel->new( 'test.xls' );
    my $worksheet = $workbook->add_worksheet();

    $worksheet->write( 'B2', 3 );
    $worksheet->write( 'B3', 5 );


    my @cols = ( 1, 2 );
    my $row  = 3;

    my $i = 1;

    for ( @cols ) {
        my $s = xl_rowcol_to_cell( 1,        $i );
        my $e = xl_rowcol_to_cell( $row - 1, $i );

        my $range = "$s:$e";
        print "$i:Range:$range\n";
        $worksheet->write_formula( $row,     $i, '=MAX(' . $range . ')
+' );
        $worksheet->write_formula( $row + 1, $i, '=AVERAGE(' . $range 
+. ')' );

        $i++;
    }


    __END__
[download]

Spreadsheet::WriteExcel does sometimes mis-parse complex formulae resulting in an invalid 0 result. However, that isn't the case here.

* You should have done this when asking the questing. It only takes a few extra lines of code.

--
John.