I use a weighted average. Weights reflect the contribution of each assignment to your final average. An assignment weighted 20 counts twice as much as one weighted 10.
Many instructors use a percentage based grading scheme.
In a generalized weighting scheme, which I use, the weights do not add up to any specific number. The details of grade calculation will be discussed later in this document , after I cover a few related topics. Percentage based grading works well when the mix of projects, exams, homework and quizzes is known in advance. I prefer to tailor the number of homework assignment and quizzes to the individual class. A percentage based scheme does not work well in this environment.