title: Getting average of top 30% of the values in one column
body: <p>I have a column that lists bunch of numbers. How can I select the average of top 30% of the values in one column:</p>
  
  <pre><code>'Values'
  10
  9
  8
  7
  6
  5
  4
  3
  2
  1
  </code></pre>
  
  <p>so, the top 30% is '10, 9, 8' and the average is (10+9+8)/3 = 9</p>