When the radius of a sphere is doubled, what is the resulting change in volume?

V=4/3pir^3
r=>2r
V=4/3pi8r^3=(32pir^3)/3

How do you calculate the mean (average) ?
Isn't it just

  Mean = (total points of all the tests) divided by (number of tests)  ?

Let's work with that.

Multiply each side of that formula by (number of tests), and you have

       Total points of all the tests  =  (Mean) times (number of tests).

In this problem, you know the mean, and you know the number of tests,
so you can easily calculate the total points.