Amy´s grade was the 90 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?
If Amy was 90th percentile out of 80, there were 72 scores below hers.
If Amy had 19 scores above hers in another class, 81 were below hers.
Total population: 180
Scores below Amy's: 72 + 81 = 153
153/180 = 85%