This short program: #!/usr/bin/perl use warnings; use strict; use List::Util qw(sum); my %h = (1 => 5, 2 => 7, 5 => 18); my $sk = List::Util->sum(keys %h); my $sv = List::Util->sum(values %h); print("Sum of keys: $sk\n"); print("Sum of values: $sv\n"); my @lk = (12, 3, 8); my $lks = List::Util->sum(@lk); print("Sum of lk: $lks\n"); yields the following output: Argument "List::Util" isn't numeric in subroutine entry at ./test1.pl line 9. Argument "List::Util" isn't numeric in subroutine entry at ./test1.pl line 10. Sum of keys: 8 Sum of values: 30 Argument "List::Util" isn't numeric in subroutine entry at ./test1.pl line 16. Sum of lk: 23 What's wrong? STFThread Next