If you have two 100 point tests and a 20 pt quiz all in the same category, it takes the percentages of each assignment and evenly averages each percentage. The 20 point quiz has as much weight as each test. Any assignment you put in a category when you have weighted categories has the same weight as any other assignment. I noticed this in my Tests and Quizzes category when two 100 point tests and a 9 point quiz averaged out to a really low grade when the quiz was missing.
Is this the way it averages grades within categories, or have I clicked a wrong button somewhere?