90th percentile out of 80

[andy123]

Angela's grade was in the 90th percentile out of 80 grades in her class. In another class there were 19 grades higher than Angela's. If nobody had Angela's grade, then Angela was what percentile of the two classes combined?
a. 72
b. 80
c. 81
d. 85
e. 92


Tried searching ...has not yet been solved..

I solved it doiing:

number of students less then angela = 71 ..in class 1

no of students less then angela = 80-19 = 61 -60 = 60 below her in class 2

thus : 71 + 60 = 131

( x/100)*160 = 131

=> x = (131 * 100 ) / 160 = 81 .87 .. = 81

but the answer is not 81 .

[scoobydooby]

whats the source?

i guess, we are missing some information. we do not have the number of students in the other class-for which 19 scores are higher than angelas

[Gmat09_5ALL]

I solved it this way :

90 % of 80 = 72 , so Angela is at 8 position. so student before her in class 1 are 7 and in class 2 are 19. so, in both the classes 26.

160-26 = 134

X = (134/160)*100 = 83.7 near to 85. Method does not seems to be correct as the answers are exact values.
Experts please suggest.

[gmat620]

Is it A ?? plz tell me because I am not sure of my method.

[life is a test]

Angela's grade was in the 90th percentile out of 80 grades in her class. In another class there were 19 grades higher than Angela's. If nobody had Angela's grade, then Angela was what percentile of the two classes combined?
a. 72
b. 80
c. 81
d. 85
e. 92

IMO D

if 10% = 8 (class 1) then 19 = 23% (rounded for class 2).
To get avg of 2 classes I did (23%+10%) /2 = 15%. 100%-15% = 85%

OA pls.

[andy123]

OA is D ..

[prabhaharan]

Class 1=> Amy's rank is 80*0.9=72 out of 80
Class 2=> Amy's rank is 81 out of 100
Combined=> Amy's rank (72 + 81) out of (80 + 100)=

(153/180)*100= 85 percentile

[Matt@VeritasPrep]

This is an unanswerable question.

To see why, consider two extreme cases.

First, suppose that Angela's classes consist of 80 and 20 people, respectively, and that there is NO overlap between the two classes other than Angela herself, so there are 99 total grades. In that case, there are 26 people who scored ABOVE Angela out of 99, so she's 27th out of 99.

Now suppose that Angela's classes consist of 80 and 1,000,000 people, respectively, and that again there is NO overlap between the two classes other than Angela herself. Then Angela is 27th out of 1,000,079 people. Think she's in a slightly higher percentile this time?

To solve, you'd need to make an assumption (like Andy did) that each class consists of 80 people, and there's essentially no overlap between the classes ... but that seems like a significant assumption.