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# Amy's grade was 90th percentile of the 80 grades for her

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Senior Manager
Joined: 02 Dec 2007
Posts: 432

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09 Oct 2008, 09:07
Amy's grade was 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 of two classes combined?

A) 72nd
B) 80th
C) 81st
D) 85th
E) 92nd

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Intern
Joined: 27 Sep 2008
Posts: 15

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09 Oct 2008, 09:18

Explanation:
==========
In the first class Amy's percentile is 90.

In the second class, amy's percentile is obviously 81.

the combiled avg percentile is 85.

thanks
SM
Manager
Joined: 15 Apr 2008
Posts: 159

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09 Oct 2008, 09:19
1
KUDOS
Nihit wrote:
Amy's grade was 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 of two classes combined?

A) 72nd
B) 80th
C) 81st
D) 85th
E) 92nd

My answer is D (85th percentile)

this is how i did it. Combining the grades of both classes, there are 27 grades above amy. finding the percentile of 27 grades gives us 15 percentile. so 15 percent grades are above her so amy is at the 85th percentile.

let me know if the answer is correct.
Senior Manager
Joined: 02 Dec 2007
Posts: 432

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09 Oct 2008, 09:32
Can anyone explain how to do this question by weighted average method?
Senior Manager
Joined: 04 Jan 2006
Posts: 276

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09 Oct 2008, 10:30
Nihit wrote:
Amy's grade was 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 of two classes combined?

A) 72nd
B) 80th
C) 81st
D) 85th
E) 92nd

Find Amy's real position in her class.

90% / 100% = x / 80
x = 90 * 80 / 100
x = 72

Amy's rank is 72. So, there are 8 people who above her.

In another class, there are 19 people who above her.

Total students = 80 + 100 = 180
Her rank when two classes combined = 180 - 19 - 8 = 153

Her percentile = 153 x 100% / 180 = 85th

Senior Manager
Joined: 04 Jan 2006
Posts: 276

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09 Oct 2008, 10:42
Nihit wrote:
Can anyone explain how to do this question by weighted average method?

The weighed average method should not be used because there is no arithmetic mean involved in this questions.

--== Message from GMAT Club Team ==--

This is not a quality discussion. It has been retired.

If you would like to discuss this question please re-post it in the respective forum. Thank you!

To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative | Verbal Please note - we may remove posts that do not follow our posting guidelines. Thank you.
Re: gmat prep question   [#permalink] 09 Oct 2008, 10:42
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# Amy's grade was 90th percentile of the 80 grades for her

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