:9.  An instructor of a class of 10 people gives a quiz with a
maximum possible score of 20 points.  He gets the following
distribution

 Score Percentage

  20 40% 
  15 30%
  10 20%
   5 10%

The average score is

 a.  12
 b.  14     
     c.  15
 d. 18 
 e.  20