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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