It's dangerous to repeatedly add decimal numbers since many of them are periodic in binary and therefore cannot be stored precisely. This includes 0.2.

>perl -le"printf '%.17f', .2
0.20000000000000001
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The following is a safer, simpler and easier to read (since "5" actually appears) version of your second snippet:

use List::MoreUtils qw(part);
my @array = (1..100);
my $i; my @parts = part { ($i++)/5 } @array;
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