GRE Quant question walkthrough: Weighted average problem

In this video, Achievable GRE course author Matt Roy shares how to solve an average when inputs are weighted differently – a common question type on the GRE Quantitative section.

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Full GRE Quant question walkthrough: Weighted average problem video transcript:

00:00:02
Here we have a weighted average problem. So let's read the question to see what clues there are that let us know that we should use the weighted average equation. So it asks what was Lennox's final grade if they scored a 95 on the midterm, a 90 on the final exam, and 82 on practice sets. Now. It also says that the 1st grade is weighted at 27%.
00:00:30
For the midterm and for the final, it's weighted at 35% and for the practice sets we're at 38%. It's intentionally worded strange here. It says the final grade is weighted at this much. That just means you're the grade at the end of the semester is your final grade. And then when it says the wait for the final, that's a final exam, so.
00:00:58
In order to find an average, usually you take the sum over the number of elements or things that are being added together. But in this case the the question specifically states that we have weights. So we should not add up the three scores and divide it by three. We should add up the three scores but multiply them by their weights. So our midterm score is 95, but the weight for the midterm is.
00:01:28
27%, so we should multiply 90 by .27 and we should do the same for the rest as well. So the final the final exam score was 90 and the weight was 35, so that's and after after the 95 times .27 we get 90 * .35. And then we do the same for the practice sets, 82 * .38.
00:01:57
Those percentages, by the way, must always add up to 100%. Anytime you're doing a weighted average problem, make sure all of your percentages add up to 100, and 2735 and 38 do add up to 100. So 95 times .27 gives you 25.6590 * .35 gives you 31.5 and 82 * .38.
00:02:26
Gives you 31.16. This sums up to be 88.31. That would be your final grade. However, it does ask you to round. It says round to the nearest whole number. So our final answer would be 88.
00:02:46
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00:03:16
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Tyler York

18 Jun 2023, 3 min read