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How do I compute my grade? (page 1 of 2)

Sections: Basic computations, Weighted grades


Different grading scales work in slightly different ways, but students' concerns usually boil down to "What do I need to get on the Final in order to pass the course or to get a certain grade overall?" This page will demonstrate the general methodology of how to answer this question.

The simplest grading scheme is one that involves cumulative points. To find out where you are, you just add points.

  • A student has earned 76 points (of the 125 points available) on the homework, 102 of 200 points on the Midterm, and 35 of 75 on the lab quizzes. The grading scale is as follows: A: 540 points, B: 480 points, C; 420 points, D 360 points. The Final is worth 200 points. He isn't worried about his grades so far, because he figures he can "pull it out" on the Final. What is the highest course grade the student can get? What grade is he likely to get?
  • So far, he has 76 + 102 + 35 = 213 points (of the 400 points so far awarded).

     

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    To get an A, he would need an additional 540 213 = 327 points, but the Final is only worth 200 points. So he can't get an A.

    To get a B, he would need an additional 480 213 = 263 points, which is also not possible.

    To get a C, he would need an additional 420 213 = 207 points. Numerically, this isn't possible, but maybe his teacher would bump his grade if he got that "close". (That is, if he got a perfect "200 of 200" on his Final, the teacher might bump his grade up to a C as a reward for having improved so much.)

    To get a D, he would need an additional 360 213 = 147 points. The Final has 200 points, so it is numerically possible for him to get a D.

    However, to get the D overall, he would need to get 147 200 = 0.735 = 73.5% on the Final. Looking at the points he's earned so far out of the points possible, he's only gotten 60.8% on his homework, 51% on his Midterm, and 46.7% on his quizzes. It is highly unlikely that he will raise his performance up to a 73.5% on the Final.

      Numerically, this student could conceivably get a D, but he'll probably get an F. He should have dropped the course back when he had a chance.

This example shows why it's important to invest a lot of effort early on in the course, while your mind is still fresh. In all my years of teaching, I've never yet seen a student "pull it out" on the Final, but I've seen many flunk trying. Don't wait until the end; learn the material up front and on time.


A point-based grading scheme might have the course grade given in terms of percentages, but the computations will mostly be the same.

  • A student has earned 112 points (of 125 points available) on the homework, 196 of 200 on the Midterm, and 68 of 75 on the lab quizzes. The course grade is out of 600 points, with the Final being worth 200 points. She wants an A, and the grading scale is as follows: A: 91%, B: 82%, C: 73%, D: 64%. Can she get an A in the course? If so, what does she need to get on the Final? If not, what is the highest grade she could get?
  • She has so far earned 112 + 196 + 68 = 376 of the 400 points so far completed; in other words, she so far is running a 94% in the course.

    To get an A overall, she needs 91% of the 600 total course points, or 546 points. That is, she needs an additional 546 376 = 170 points. Since the Final is worth 200 points, she needs 170 200 = 0.85 = 85% on the Final.

    Since she has 112 125 = 90% on the homework, 196 200 = 98% on the Midterm, and 68 75 = 91% on the quizzes, she should be able to get an A in the course. That is, given her past performance, it is reasonable to expect that she can do sufficiently well on the Final to get the grade she's hoping for. And even if she has a "brain fart" on the Final, she shouldn't do worse than a B overall.   Copyright Elizabeth Stapel 2004-2011 All Rights Reserved

      She can get an A in the course, but even if she has trouble on the Final, she shouldn't get lower than a B.

The two grading schemes above are pretty easy to compute. To find out how you're doing in any grade component's subscore (for homework, for instance, or for the quizzes), you just divide the points you've earned by the points that have so far been awarded to get your percentage on that subscore. To find out what you need on the Final, you add up the points you've earned so far in each grade component. You subtract this from the number of points necessary for the grade you're wanting to get overall. Then divide the result by the number of points on the Final, to get the percentage grade you need on the Final. And you can evaluate how reasonable that Final percentage grade is by comparing it with your subscore percentages.

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Cite this article as:

Stapel, Elizabeth. "How Do I Compute My Grade?" Purplemath. Available from
    http://www.purplemath.com/modules/howgrade.htm. Accessed
 

 



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