Problem Solving

Can someone please help me out with this percentile problem.

Amy's grade was the 90th percentile of the 80 grades for her class.Of the 100 grades from another class,10 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?

1) 72nd
2) 80th
3) 81st
4) 85th
5) 92nd

90th percentile out of 80 means that there were 8 more grades that were higher than Amy's
And there were 19 higher than Amy's grade out of 100
The total amount of people=100+80=180
The total amount of people with grades higher than Amy's=19+8=27
So, 153/180=85th percentile

D

Thanks a lot Lilu....

I understand where you're getting the 8 from (.1 * 80)...can you please explain the logic behind 19?

It's supposed to say that 19 were higher than Amy's - not 10.

Just a typo.

VP_Jim wrote:It's supposed to say that 19 were higher than Amy's - not 10.

Just a typo.

Thanks! I was just thinking..that my answer(10+8)--> 162/180--> 90% ) 90% is not in the answer. Thanks Jim.