百分位数（percentile）也是一个很常考察的概念，下面是官方指南（OG）的介绍：
For data listed in increasing order, the percentiles of the data are 99 numbers that divide the data into 100 groups that are roughly equal in size. The 25th percentile equals the first quartile; the 50th percentile equals the second quartile, or median; and the 75th percentile equals the third quartile.
JJ（后有参考过程及答案）：
1. In a data set of 10,000 numbers varying from 20 to 80, the number 62 is the 60th percentile and the number 74 is the nth percentile.（2015.5.10原题）
Quantity A: n
Quantity B: 70
2. In a data set of numbers, the number 48.5 is the 50th percentile and the number 56.5 is the 60th percentile.（6.5）
Quantity A Quantity B
the number at the 40thpercentile 40.5
（原文：那个50th是48.5，60th是56.5，问40th时跟40.5比大小）
3. （OG例题）（7.21考到了类似的）
4. （OG例题）
5.（OG例题）
参考答案：
1. D
2. D
3. D
4. B
总结：
一般不说明如何分布的时候，是无法知道相应百分位数的具体大小（而例题4属于正态分布，即normal distribution）
4题官方解析：
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