How to calculate the Percentile

[ashforgmat]

154) 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


please can some help with the explanation of the above.

Thanks.

[addy100]

First calulate how many students are ahead of him i.e. in class a out of 80 8 are ahead of him since he is having 90 % .
second class has 19 students having more per than him . so total stduent in both class comes to 190 and 27 students have higher per than him . so automatically he is having 85% if we compare for both class.

[ajith]

154) 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


please can some help with the explanation of the above.

Thanks.

If Angela was at 90th percentile - 90% of the students' grade were below Angela's

so Angela's rank was 8 and there were 7 students above angela in her class

Now assuming that the second class also had 80 students

The combined rank of Angela will be 27

There will be 160-27 = 133 students with grades less than Angela

The percentile would be = 133/160*100 = 83.1

Which is not in the answer choices

[ashforgmat]

Now i am confused as to which is the correct explanation....

[ajith]

Now i am confused as to which is the correct explanation....

May I know the source of the question.

if you are at 90th percentile on some parameter means 90% of the group is below you on that parameter.
So in a class of 80 if you are at 90th percentile - 90% i.e. 72 students are below you.

[ajith]

https://en.wikipedia.org/wiki/Percentile

[ashforgmat]

The source is 198 maths questions 700+...

[agresj]

IMO it seems as if there's a missing variable that needs to be defined. You need to somehow derive the total number of students in the other class. Without that, the problem doesn't make much sense. If there are only 19 people in the other class the final percentile will be much different from if the other class had 1000 students.

[krazy800]

Plz check the link below

https://www.beatthegmat.com/percentile-t ... tml#139703

HTH!

[ajith]

Plz check the link below

https://www.beatthegmat.com/percentile-t ... tml#139703

HTH!

I totally disagree with the explanation in that link even though I agree with the answer

Angela is at 90th percentile means there are 72 students (90/100*80) below Angela! or there are 7 above Angela
In the other class there are 19 Above Angela out of 100

Angela's combined rank is 27 and there are 153 students (180-27) below Angela hence the percentile is 85%

The explanations in the above link is wrong because they assume that 90th percentile means there are 10 percent above Angela wherein it actually means 90 Percent are below Angela.

Somehow it doesn't alter the answer though!