How to Calculate a Needed Final Score
Suppose you want to know what score you’ll need to raise your final grade by a letter. For example, suppose you know that your average in a class is 87.3 and you want to get an A. So you need to know what final exam grade you need in order to get an 89.5, which will round to an A. You can easily arrive at the answer if you know the weights of the exams. Of course, don't assume that your teacher will round up. You may need to get a 90.0 in order to get an A.
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Instructions
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1
Decide on the final grade that you want, and denote it with the letter F. For example, suppose you want a B. Then F=79.5 percent. Make sure that, in your school system, the instructor would in fact round up 79.5 to an 80. If your grade system needs, say, an 84 and there is no rounding up, then set F to 84.0.
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2
Multiply the weight of the grades so far by the average of those grades. For example, if the final counts for 25 percent of the final grade, then the weight of the grades preceding it total 75 percent. If the grade average so far is 72 percent, then the product of the two is 0.75x0.72 = 0.54.
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Subtract the result of Step 2 from the result of Step 1. Then divide by the weight of the final exam to get your answer.
For example, 0.795 - 0.54 = 0.255. Now divide this by the weight of the final exam, 0.25, to get 1.02. This means that you’ll need 102 percent on the final to get a B for the course. The only way to get it is if there is extra credit on the exam.
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Tips & Warnings
The effective formula that you used above was [ weight of prior grades x average of prior grades + weight of final x grade of final ] = grade for class. The grade of the final exam was unknown, but the other terms were known, so you could solve for the minimum final grade using algebra, making the grade of the exam the unknown.
