In the spirit of TIMTOWTDI, a different approach using sort, grep and map in a do block.

use strict;
use warnings;

my %Ave =
   map { $_ => rand }
   q{a} .. q{z};

print do
   {
       my $count = 0;
       map  { qq{$_\t$Ave{ $_ }\n} }
       grep { $count ++ < 20 }
       sort { $Ave{ $a } <=> $Ave{ $b } }
       keys %Ave;
   };
[download]

I hope this is of interest.

Cheers,

JohnGG