Using 'Weighted mean of grades'

The first feature of the new grade book that I found myself wanting to be able to master is the ability to 'clump' assignments into categories and then have each category be assigned a different weight in the overall final grade. (Note - I'm using the term 'clump' and avoiding the term aggregate to prevent confusion given the terminology used in the new grade book)

Example (how some classes are evaluated at my school)

Attendance & Participation 40%, Quizzes 20%, Tests (Mid-term & Final) 20%, Final Projects 20%,

For this short doc I'll just use two categories (Reading and Writing) and 4 Assignments (offline activity).

So after creating the 4 assignments this is what it should look like (roughly).