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标题: 一道奇怪的prep题 [打印本页]

作者: butterfly08 时间: 2007-12-17 17:44
标题: 一道奇怪的prep题

Amy's grade was the 90th percentile of the 80grades for their 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 grade of the two classes combined?

ans: 85th

几乎没有看懂题的意思，请高人指点思路

谢谢！

作者: wwfirst 时间: 2007-12-17 18:04
amy在自己班上80人中属于90百分点，也就是80人中她排第8(80*(1-90%))，7人超她。另外一班100人中19人分数超过她，其余人都比她低，问两班合起来她排多少百分点。

两班合起来180人，低于她的有153人。

所以，153/180=0.85

作者: mych666666 时间: 2007-12-18 01:23
同意楼上，我当时也没回过神来，不过后来仔细一想就是这样，关键是不要认为90%percent 是top 90%.

作者: butterfly08 时间: 2007-12-18 12:05
恩没错！谢谢

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