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
percentile=成绩比他低的数/总成绩个数*100%
成绩比amy低的人数是80*90%=72,另外一个班19个比他高,81个比他低,加在一起比amy分低的人数是72+81=153
percentile=153/180约等85%
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