prep2-ps-148

飞不高

以下是引用mchome在2009-5-31 14:40:00的发言：

148. 15080-!-item-!-187;#058&010499
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?

(A) 72nd
(B) 80th
(C) 81st
(D) 85th
(E) 92nd

答案D，哪位指点下怎么做的？

thx！

her class, amy grade 90th of 80, 意思是在她前面有8个（80*10%），另一个班19个higher than amy's

the combined number of higher than amy's 27,

(100+80-27)/180=85%