G的数学题,

题目

G的数学题,
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 two classes combined?
题意不懂,
那这个题目是讲什么啊？
不是求的百分数啊，答案是85th

答案

答案是不是
(80*0.1+19)/(100+80)=0.15
即15%?
噢算反了
这是在Amy前面的人占15%
剩下的占85%
答案是85th percentile of all