use Data::Dumper;

sub getRange
{
  my $value = shift;
  warn "Unexpected value $value," and return if $value < 1;
  return '1-19' if $value < 20;
  return '20-29' if $value < 30;
  return '30-39' if $value < 40;
  return '40-59' if $value < 60;
  warn "Out of range value $value," and return;
}

my %hits;

while (<DATA>)
{
  my $range = getRange($_);
  $hits{$range}++ if defined $range;
}

print Dumper \%hits;

__DATA__
12
14
15
20
21
50
42