for file in *.txt
do
   gawk -v p=50 '
    {a[sprintf("%07d",$3)]}
    END{
      asorti(a,as)
      end=length(a)
      start=end-int(end*p/100)+1
      if(start>end) start=end
      printf("File has %d unique values, average from %d to %d\n", end, start, end)
      for(i=start;i<=end;i++) total=total + as[i]
      printf "%s\t%.2f\n", FILENAME, total/(end-start+1)}' "$file"
done