title: Using awk to calculate average of grades
body: <p>I have a file like this:</p>
  
  <pre><code>id1 name1 grade1 grade2 grade3....gradeN
  id2 name2 grade1 grade2 grade3....gradeN
  etc
  </code></pre>
  
  <p>and I want to print the id, name and average of grades of each row using awk.
  any idea?
  the output should be like:</p>
  
  <pre><code>id1 name1 avg_of_grades
  id2 name2 avg_of_grades
  </code></pre>