How to compute your final grade

What do I have to get on the final to get an A?

This page discusses the relationship between your grade before the final, your grade on the final, and your overall course grade. With this you can compute what your grade would be, depending on what you get on the final.

The "equation"

Since the final exam is worth 30% of the course grade, everything up to that point is worth 70%. The following formula gives this relationship:

.7 * (Grade so far) + .3 * (Final exam grade) = Course grade

Look scary? It doesn't have to! All you need is a little bit of algebra, the part where you simplify equations to find an answer. In this case, you already know (if you ask me) what your "Grade so far" is, so if you pick one of the other two variables, say what you want your course grade to be, then you are just solving the equation.

Solving the equation

Solving for a final exam grade

Suppose you have an 87.44 so far in the course, and you want to get at least an A- (90.00). Here is our equation:

 .7 * 87.44 + .3 * (Final exam grade) = 90.00

61.208 + .3 * (Final exam grade) = 90.00

.3 * (Final exam grade) = 28.792

Final exam grade = 28.792 / .3 = 95.973

So you would need almost a 96 on the final to get an A-.

Solving for a course grade

Let's do another example, this time trying to figure out the course grade from a final exam grade. Imagine you have a 91.23 so far, and you want to know what would happen if you got an 85 on the final exam:

.7 * 91.23 + .3 * 85.00 = Course grade

63.861 + 25.5 = 89.361

In this case, your grade would be just over 89, or a B+.

Wait a minute, I thought you said the final was worth a big part of our grades!

Why doesn't our grade change very much, even if we do really well on the final?

It turns out that the final can't raise your grade too drastically, if you've been keeping up with the course: you can't go from a C to an A+ just with a good final exam. But your grade can drop pretty far if you don't do well: even if you got a perfect score on everything up to the final, the best you could do would be a 70 if you skipped the final. If you had a 93.33 before the final, an A, and then brushed off the final and got a 50%, what would your grade be?

.7 * 93.33 + .3 * 50 = 80.33

Your grade would go all the way from an A down to a B- (and barely above a C+)! So it is important to do well on the final. It is possible to raise your grade by doing well, but it is also possible to severely hurt your grade by not preparing for the final.

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