One of your friends at Harvard complains that the average class size at
Harvard is too big. He bets that your average class size is much smaller.
You decide to see if he is correct. Unfortunately, you are not sure how to
measure average class size.
Your first idea is to see if the registrar will give you a list of all the
classes this term and the size of each classes. Then you will just average
these to get average-class-size-1.
But then you have another idea. ``I'm a rather typical student and taking
three courses. Why don't I just take the average of the sizes of my
courses?" Then you worry that perhaps you are not completely typical so you
decide to ask a bunch of students to do this and take the average of their
responses. Better yet, you ask the registrar to do this for every student
and give you the average of all student averages. That surely should be what
your friend would mean by the average class size. You call this
average-class-size-2.