Amy's grade was 90th percentile of the 80 grades for her

AAPL wrote:GMAT Prep

Amy's grade was 90th percentile of the 80 grades for 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 what was percentile of the grades of the two classes combined?

A. 72nd
B. 80th
C. 81st
D. 85th
E. 92nd

OA D

Given that Amy's grade was 90th percentile of the 80 grades, it means that she outscored 90% of 80 = 72 scores.

Similarly, in other class, since 19 scores were higher than Amy's, and the rest were lower, she outscored 100 – 19 = 81 scores

So, out of a total grade 80 + 100 = 180, she outscored 72 + 81 = 153 scores

Amy's percentile = 153/180 * 100% = 85th %ile

The correct answer: D

Hope this helps!

-Jay
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AAPL wrote:GMAT Prep

Amy's grade was 90th percentile of the 80 grades for 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 what was percentile of the grades of the two classes combined?

A. 72nd
B. 80th
C. 81st
D. 85th
E. 92nd

OA D

Since Amy’s grade is in the 90th percentile of the 80 grades in her class, 10% of the number of total grades in her class are not lower than Amy’s grade, i.e., 8 grades. Note that these 8 grades include Amy’s own grade. When combined with the number of grades from the other class, there are 8 + 19 = 27 grades that are not lower than Amy’s grade, including Amy’s own, in a total of 80 + 100 = 180 grades. Since 27 / 180 = 0.15, this amounts to 15% of all the grades. Therefore, Amy’s grade is the 100 - 15 = 85th percentile of the combined grades of the two classes.

Answer: D