一道PREP的题目...求大家帮忙解答一下吧....

lw666777

percentile的概念一直搞不清楚...
哪位帮忙解答一下吧...


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 classes combined?

ANSWER:85th

Libbyyao

90th percentile说明80个人中 90%的人分比她低，也就是72个人，则她排在第8名，前面7个人分比她高
再和别的班级比较，19个人又比她高，说明两个班加起来一共7+19=26人分高于她 ，她排在180个人的第27名
比她低的人有180-27=153人 153/180 x 100%=85% 就是她在合起来两个班中的percentile.
呵呵不知道有没有讲清楚~

lw666777

哦...原来是这个意思...谢谢谢谢...