求解一道数学题，PREP里遇见的，第一题就把我砸蒙了。。

xphdp123

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 2 classes combined?
A72nd   B 80th   C 81st    D85th   E92nd

这题首先我第一句话没读懂，什么叫 was the 90th percentile of the 80 grades for her class？
再就是这道题答案选D  我选了个C。。。。真是不会做
下周三就考了，请各位指点迷津之~~
大谢~~~~~！

吉麦特小姐

我的理解是,AMY考了80分,排名是全班的90%UP,也就是说,她是全班的TOP10%. 不知道解释清楚了没.

Iljiajia

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 2 classes combined?
A72nd   B 80th   C 81st    D85th   E92nd

这题首先我第一句话没读懂，什么叫 was the 90th percentile of the 80 grades for her class？
再就是这道题答案选D  我选了个C。。。。真是不会做
下周三就考了，请各位指点迷津之~~
大谢~~~~~！

-- by 会员 xphdp123 (2010/4/15 18:03:05)

第一句话是说Amy的成绩在她们班80人中排在第90%的位置，也就是有10%的人比她成绩好，那么是8个人比她好。

第二个班有19个比她好，所以两班共8+19=27人成绩比Amy好，两个班共有180人，所以算出来是（180-27）/180=85%