Amy's grade was the 90th percentile of the 80 grades for her class. Of the 100 grades from another class, 19 was higher than Army's and the rest was lower. If no other grade is the same as Amy' grade, then Army's grade was what percentile of grades of two class combined.

A 72th

B 80th

C 81th

D 85th

E 92 nd

the answer is D

Why? give some tips

the 90th percentile of the 80 grades for her class，说明有10%的人higher than amy's,即10%*80=8个人。

另外一个班有19个人比她高

两个班总共27个人。

（180-27）/180=85/100