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

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Joined: 12 Oct 2008
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Amy's grade was 90th percentile of the 80 grades for her  [#permalink]

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Updated on: 02 Apr 2012, 17:27
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Difficulty:

35% (medium)

Question Stats:

72% (01:29) correct 28% (01:27) wrong based on 264 sessions

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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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Originally posted by reply2spg on 05 Jan 2010, 20:31.
Last edited by Bunuel on 02 Apr 2012, 17:27, edited 1 time in total.
Edited the question and added the OA
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Joined: 02 Sep 2009
Posts: 52386
Re: Prep Question..How to calculate persentile?  [#permalink]

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06 Jan 2010, 03:43
2
7
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

Being in 90% percentile out of 80 grades means Amy was 73rd (from the least grade) in the class (as long as nobody had Amy's grades), she outscored 72.

In another class her grade would rank her 82 (from the least grade out of 101, 100+Amy), 81 had the grades lower than Amy.

So in combined classes she outscored 72+81=153. There are 180 students 153/180=0.85

Answer: D (85%)
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Re: Prep Question..How to calculate persentile?  [#permalink]

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06 Jan 2010, 19:33
1
Shouldn't Amy be student 73 instead of 72? According to wikipedia, percentile is defined as:

"A percentile is the value of a variable below which a certain percent of observations fall. So the 20th percentile is the value (or score) below which 20 percent of the observations may be found."

So if Amy is in the 90% percentile, she is better than 90% of the class, which is 72 students, making her the 73rd student.
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Re: Prep Question..How to calculate persentile?  [#permalink]

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08 Jan 2010, 23:10
1
Generally being in x% means that x% has the grades less than you.

Amy in 90% --> she outscored 90% of of 80=72 (Amy is 73rd).
Of the 100 grades from another class, 19 were higher than Amy's, and the rest were lower --> rest is 81, hence Amy outscored 81.

So out of total 80+100=180, Amy outscored 72+81=153. Hence she is in 153/180=85%.
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Re: Percentile  [#permalink]

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08 Mar 2010, 08:05
2
Let me try this.

Amy’s grade was 90th percentile of the 80 grades ==> 80*90/100 = 72.
So She stands at 8th 72nd position from the bottom, that means there are 8 students with higer grade than Amy in her class.
Of the 100 grades from another class, 19 were higher than Amy’s, and the rest were lower.
When you add both the classes, it is 180 total students and 8+19 = 27 students have higer grade than Amy's.
Amy stand at 153 (180-27) position from the bottom.
To find the percentile,
180*x/100 = 153
x = 1530/18 = 85 %.

85% is the answer.
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Joined: 22 Jan 2010
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1st Question on GMAT Prep!!  [#permalink]

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12 Mar 2010, 14:44
Hi All,

Help needed for the very first question on GMAT Prep, so it must be a 500 level question! But didn't understand anything about it (Still managed to get 680 somehow!!)

Q> Amy's grade was 90th percentile of the 80 grades of her class. Of the 100 grades of 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?

72nd/80th/81th/85th/92nd
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Joined: 16 May 2009
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Re: 1st Question on GMAT Prep!!  [#permalink]

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12 Mar 2010, 15:22
In a class of 80 students she is at the 90th percentile , so there are 80 ( 90%) = 72 students ranking below her

In a class of 100 there are 81 students whose scores are below her score

number of students ranking below her / total number of students = her percentile ranking

(72+81) / 180 = 85%

I dont know why it took me so much time to figure it out!!!!!
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Re: 1st Question on GMAT Prep!!  [#permalink]

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25 Apr 2010, 09:54
thanku for the explanation Bunuel
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Re: Amy's grade was 90th percentile of the 80 grades for her  [#permalink]

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06 Jul 2016, 09:27
1
reply2spg 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

Here's my take...

Let the first class be noted as A and the second as B.

A
Total = 80
Percent scoring higher than Amy = 10...or 8 people

B
Total = 100
People scoring higher than Amy = 19

Total people in combined class = 80+100 = 180
People scoring higher than Amy = 8+19 = 27

Thus..

Amy's percentile

$$= (1 - \frac{27}{180})*100$$

Answer 85(D)

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

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10 Dec 2016, 09:55
This is one great Official GMAT prep Question.
Here is what i did in this Question =>
Amy's Rank in class 1 => 90/100 *80 => 72
Hence 8 students scored higher than her.
In class two => 19 students scored higher than her.
Hence Overall => 19+8=> 27 Students scored higher than her
And 27 is 15 percent of 180

Hence Here Percentile Rank must be 85

Hence D.

I have one doubt though.
Why is the OA above saying that her rank was 73.
What does percentile ranking mean here.?
chetan2u ??

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Re: Amy's grade was 90th percentile of the 80 grades for her  [#permalink]

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16 Dec 2018, 18:59
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Re: Amy's grade was 90th percentile of the 80 grades for her &nbs [#permalink] 16 Dec 2018, 18:59
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# Amy's grade was 90th percentile of the 80 grades for her

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