IR大全中，我个人认为这一篇的问题是最难的，很绕很绕。不知大家是否有印象，在数学的PREP中有出现过关于percentile的题目，通过这一题目我们了解了什么是percentile。回到这篇IR题目，我觉得单纯了解Percentile还是不够的，因为Percentile不难，难在我们要快速读懂题目绕来绕去的表达，以及通过估算而不是真正精确的计算去找到正确答案。
附件是我个人对这篇IR的理解，希望对大家有用。（附件回复可见）
IR大全中13-18题关于身高、年龄、体重问题的解析
另外，我在Wiki中找到的Percentile的简单定义，帮助大家简单了解；我也将数学题目中的Percentile原题及我的解析贴在此处，帮助大家对Percentile加深印象。
Percentile
•A percentile(or a centile) is a measure used in statistics indicating the value,below which a given percentage of observationsin a group of observations fall.
•Forexample,if a score is in the 86th percentile, it is higher than 86% of the other scores.
PREP2（148）原题：答案是D
Amy'sgrade was the 90th percentile of the 80 grades for her class. Of the 100 grades from another class, 19 werehigher than Amy's, and the rest were lower. If no other grade was the same as Amy's grade, then Amy's grade was whatpercentile of the grades of the two classes combined? (A)72nd (B)80th (C)81st (D)85th (E)92nd
解析：
“Amy's grade was the 90th percentile of the 80 grades for her class.”means Amy’s grade is higher than 90% of the 80 grades in her class. Wecan get the inequalities: **Amy’sgrade > 90% x 80 (grades) = 72
**Amy’sgrade > (100-19) (grades) = 81
Therefore,if the two classes combine, Amy’s grade is higher than (81+72) grades. (81+72)/180= 85% Theanswer is D.
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发表于 2014-4-25 10:04:20
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