BTGmoderatorDC wrote: ↑

Fri Feb 28, 2020 4:38 pm

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 was what percentile of the grades of the two classes of two classes combined?

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

OA D

Source: GMAT Prep

Since Amy's score is 90%ile, the number of scores less than Amy's = 90% of 80 = 72;

Given that of 100 grades from another class, 19 scores were higher than Amy's, the number of scores less than Amy's = 72 + (100 – 19) = 72 + 81 = 153

Thus, Amy's percentile out of 180 = (153/180)*100% = 85%ile

The correct answer: D

Hope this helps!

-Jay
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BTGmoderatorDC wrote: ↑

Fri Feb 28, 2020 4:38 pm

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 was what percentile of the grades of the two classes of two classes combined?

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



OA D

Source: GMAT Prep

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