Grades In Progress

Let's imagine you have a grading system where homework counts 20% of the grade (30 small assignments -- roughly two per week -- at 20 points each), the final exam counts 20% of the grade, and the remaining 60% of the grade is made up of four exams, equally weighted at 15% each.

How do you calculate a student's course average during the semester?

Let's say that a few weeks into the semester there have been eight homeworks and one exam. Stu scored 14/20 on all eight homeworks and 90/100 on the exam. What's Stu's average?

I've decided to give the WebAssign gradebook a try this semester even though it seems to calculate the grades during the semester using a method other than my preferred one. My spreadsheet does the weighting on an assessment-by-assessment basis, not on a category basis. WebAssign weights things by category. It will count your exam average as 60% of your grade no matter how many exams you've taken. This worries me because the grades that it reports to the students will be more volatile than I'd like them to be, and a lucky high score on the first exam will give students' inflated perceptions of their standing in the class.