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

Question

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

Scott@TargetTestPrep · Answer

BTGmoderatorDC wrote: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

Alternate approach:

In Amy's 80-student class, her percentile = 90.
In the 100-student class, 19 scores are higher than Amy's, implying that 81 scores are lower.
Thus:
Amy's percentile in the 100-student class = 81.

Amy's AVERAGE percentile for all 180 students = (80*90 + 100*81)/180 = (80*10 + 100*9)/20 = 1700/20 = 170/2 = 85.

The correct answer is D.

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deloitte247 · Answer

Amy was 90th percentile i.e she scored more than 90% of 80 grades = 72
Amy was 73rd from the least grade.
In another class, her grade will rank her 82 from the least grade.
She scored more than 81 grades

combining the two classes.
Amy outscored 72 + 81 = 153 students.
Given that there are 180 students
Her percentile =
$$\frac{153}{180}\cdot100=85\%$$

$$answer\ is\ Option\ D$$

deloitte247 · Answer

Amy was 90th percentile i.e she scored more than 90% of 80 grades = 72
Amy was 73rd from the least grade.
In another class, her grade will rank her 82 from the least grade.
She scored more than 81 grades

combining the two classes.
Amy outscored 72 + 81 = 153 students.
Given that there are 180 students
Her percentile =
$$\frac{153}{180}\cdot100=85\%$$

$$answer\ is\ Option\ D$$

GMATGuruNY · Answer

BTGmoderatorDC wrote: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

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