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Grades and percentiles Amy's G

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Grades and percentiles Amy's G

by enriqueta26 » Mon Jul 19, 2010 10:40 am
Could someone help me with this problem, please?

Amy's grade was 90th percentile of 80 grades of her class. Of the 100 grades from another class 19 were higher than Amy's, and the rest were lower. If no other grade was the same as Amy's grade, then Amy's grade was what percentile of the grades of the two classes combined?

Source: Gmat practice exam

[spoiler]A: 85th[/spoiler]
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by Patrick_GMATFix » Mon Jul 19, 2010 11:13 am
Enriqueta when you post, please post answer choices. Sometimes the best approach to solving requires the use of the answer choices.

Percentile is the percentage of data points that are smaller. Amy's score is 90% better than all others in her class. So there are 72 grades below hers. In the other class, there are 81 grades below Amy's. Of the 180 grades in the two classes, 72+81=153 are below Amy's. This means that 85% of grades are below Amy's. Her grade is the 85th percentile.

Two detailed ways to solve, including a way that takes 10 seconds using the answer choices, as well as a video solution are available at GMATPrep Question 1386. If you have trouble with percentiles and related topics, set topic='Statistics' and difficulty='500-600' in the Drill Generator.

-Patrick
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by enriqueta26 » Mon Jul 19, 2010 11:39 am
than you Patrick!! I will post all the answers next time I take a test.!!
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