dferm wrote:Amy's grade was the 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 combined?
A. 72nd
B. 80th
C. 81st
D. 85th
E. 92nd
Please Help....
Thanks.
Percentile means the percentage below.
Out of 80 grades, if Amy's grade was the 90th percentile, then 90% of the grades were lower than Linda's grade. Thus, .9*80 = 72 grades in Amy's class were lower than Amy's grade. Subtracting these 72 grades and Amy's grade from the total, we get that 80-72-1 = 7 grades were higher.
Since 19 grades in the other class were higher than Amy's grade, 19+7 = 26 grades in the combined classes were higher than Amy's grade. Subtracting these 26 grades and Amy's grade from the total number of grades in the combined classes, we get that 180-26-1 = 153 grades were lower than Amy's grade.
Thus, Amy's percentile in the combined classes was 153/180*100 = 85%.
The correct answer is
D.
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