>perl -wMstrict -le
"my %tiers = map { $_ => int($_ % 50 / 10) } 0 .. 99;
 ;;
 for my $n (-1, 0, 11, 22, 33, 44, 55, 66, 77, 88, 99, 100, 101) {
   print qq{tier $n },
         exists $tiers{$n} ? qq{== $tiers{$n}} : 'out of range';
   }
"
tier -1 out of range
tier 0 == 0
tier 11 == 1
tier 22 == 2
tier 33 == 3
tier 44 == 4
tier 55 == 0
tier 66 == 1
tier 77 == 2
tier 88 == 3
tier 99 == 4
tier 100 out of range
tier 101 out of range