You need to capture the results returned from your subroutines

my $av = aver();
my $min = min();
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Then just make sure to return a value in your min subroutine.

sub min {
    my @num = @_;
    my $min;
    ...
    return $min;
}
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Finally, you would be much better off if you had use strict at the beginning of your code.

- Miller