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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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80*(1-90%) =8 →There are 8 people ahead of Amy in her class
Combined with another class, there are 19+8=27 people’s grades ahead of Amy’s.
# of people whose grades below Amy’s / total people of twp class → (100+80-27)/(100+80)=85%
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