GMAT Prep - Amy's Grade

tutonaranjo wrote: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

Answer is D
No idea what this means or how to set it up. Supposedly easy.
Appreciate a detailed explanation.

jaspreet.sharma wrote:

tutonaranjo wrote: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

Answer is D
No idea what this means or how to set it up. Supposedly easy.
Appreciate a detailed explanation.

Amy's grade was the 90th percentile means people above Amy are 10
from another class, 19 were higher than Amy's, This means total 10 + 19 people are above AMy

This means 100- (29/ 180 ) is the new percentile of Amy = approx 85

So answer is D