Or skip the hardcoded server count assumption.

my %clustertotal;
my %clustercount;
foreach my $servername (keys %servers) {
    $clustertotal{$servers{$servername}}    += get_cpu($servername);
    $clustercount{$servers{$servername}}++;
};

print "$_:\t".($clustertotal{$_}/$clustercount{$_})."\n" foreach sort 
+keys %clusters;
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