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| Math Central | Quandaries & Queries |
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Question from Cindy, a parent: We need to weight numbers differently in terms of a percentage calculation. One number {80 for example} at 65% and another number {100 for example} at 35%. How do we calculate these into one total grade for example. |
Hi Cindy,
You should probably ensure that the two grades are on the same basis. So, for example suppose the score on the first assignment was 80 out of a possible 90 and the score on the second assignment was 100 out of a possible 120. To scale each of them so they are out of a possible 100 I would do the following
- 80 out of 90 becomes 80/90 ×100 = 88.89
- 100 out of 120 becomes 100/120 ×100 = 83.33
The first assignment is weighted 65% 0r 0.65 and the second assignment is weighted 35% or 0.35 so the weighted sum, out of a possible 100 points is
88.89 × 0.65 + 83.33 × 0.35 = 86.95
I hope this helps,
Penny
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