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题库 / Prep2007E2-PS-148
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 classes combined?
72nd
80th
81st
85th
92nd
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There's also the brute force method, which doesn't take that much time here.
Amy's grade is 90th percentile, meaning that she outperformed 90% of her classmates. That means that she outperformed 72 of her classmates.
She also outperformed 81 of the students in the other class (note: not 80, because Amy herself is not in the other class).
This means that she outperformed 72 + 81 = 153 of the combined 180 students in the two classes.
Since 153/180 = 0.85, she outperformed 85% of the students in the combined pool, putting her in the overall 85th percentile.
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