title: Remove a known number of documents from Mongo database
body: <p>I have a very big database in Mongo. It has more than 69 000 documents.</p>
  
  <p>I took the decision to remove the majority of them. I want to have just 10 documents, for example.</p>
  
  <p>How can I randomly remove a number of documents from database inside of terminal (directly)?</p>
  
  <p>I've already tried <code>db.col_name.remove().limit(20)</code> which is not working.</p>