How do you figure out what you need to get on a final to earn a certain grade?

Answer 1

Chuck be has got it. Here is how I figure it out, slightly differently and maybe easier to understand.

Let's say you currently have 75% from everything before the final, and you want to get 90% in the class for a final grade of A-. Let's also say that the final is worth 20% of your grade, and therefore everything before is 80% of your grade.

0.8*75 + 0.2*F = 90

F is the grade on the final, and in this case, solving for F gives you 150, and unless there is massive extra credit on the test this means that an A- is impossible.

Let's see the highest possible grade you can get, if you get 100 on the final.

0.8*75 + 0.2*100 = 80

So if you have 75% going into the final, the highest grade you can possibly get is 80, a B- in an unweighted system. If grades are weighted it is impossible to do this calculation because your grade depends on how everyone else does as well.

Answer 2

You would have to know 3 things:
A) The weighting of the final exam.
B) The current grade average
C) The desired final grade average.

Let's say, for instance that you are currently carrying an 80% average (item B = 80%). Let's say that the final exam counts for 25% of your final grade (item A = 25%). And, finally, let's say that you want to have an 85% average after the final exam (item C = 85%).

Use the following formula:

(A / 100)x + (((100 - A) / 100)B) = C

so, using the values above:

(25 / 100)x + (((100 - 25) / 100)80) = 85
.25x + ((75 / 100)80) = 85
.25x + (.75(80)) = 85
.25x + 60 = 85
.25x = 25
x = 100

So, you would have to have a 100% on your final exam to end up with a course average of 85%.

Hope this helps.

Answer 3

Two intelligent solutions have been given. Choose either one./ I prefer the second.