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问一道数学PREP08

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发表于 2012-2-21 18:35:48 | 只看该作者 回帖奖励 |倒序浏览 |阅读模式
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 81th
d 85th
e 92nd

选d,能反过来推算到,但做的时候总觉得这个题意不理解啊,还是第一道。有达人能解释一下嘛?
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