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Amys grade was the 90 percentile of the 80 grades for her

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Senior Manager
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30 Jan 2008, 11:23
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Amy´s grade was the 90 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 combined?

A) 72
B) 80
C) 81
D) 85
E) 92

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Senior Manager
Joined: 29 Nov 2006
Posts: 318

Kudos [?]: 162 [0], given: 0

Location: Orange County, CA

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30 Jan 2008, 11:29
Quote:
Amy´s grade was the 90 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 combined?

A) 72
B) 80
C) 81
D) 85
E) 92

D

If Amy was 90th percentile out of 80, there were 72 scores below hers.
If Amy had 19 scores above hers in another class, 81 were below hers.

Total population: 180
Scores below Amy's: 72 + 81 = 153

153/180 = 85%

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Director
Joined: 01 Jan 2008
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30 Jan 2008, 11:33
netcaesar wrote:
Amy´s grade was the 90 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 combined?

A) 72
B) 80
C) 81
D) 85
E) 92

D - 85%.

number of grades not exceeding Amy's (72+(100-19))
total number of students 80+100
percentile: (72+81)/180=153/180 = 85%

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CEO
Joined: 29 Mar 2007
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30 Jan 2008, 13:55
netcaesar wrote:
Amy´s grade was the 90 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 combined?

A) 72
B) 80
C) 81
D) 85
E) 92

She is 72/80 in the first and 80/100 in the second.

Thus there are 27 people ahead of Amy. 180-27=153 ---> 153/180~85%

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SVP
Joined: 28 Dec 2005
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30 Jan 2008, 18:59
in her class, she is in the top 8, i.e. 72 people scored lower than her

in the second class, she is in the top 19, i.e. 81 people scored lower than her

overall, she is 153/180 (you get 153 because shes scored higher than a total of 72+81=153 ppl)

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SVP
Joined: 04 May 2006
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30 Jan 2008, 19:14
maratikus wrote:
netcaesar wrote:
Amy´s grade was the 90 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 combined?

A) 72
B) 80
C) 81
D) 85
E) 92

D - 85%.

number of grades not exceeding Amy's (72+(100-19))
total number of students 80+100
percentile: (72+81)/180=153/180 = 85%

Hi everybody,

I am very confused with this problem. The question is about "Amy's grade was what percentile of the grades of the two classes combined?", but guys all of you go to find the grades of not exceeding Amy's, and then credit it with what question asked. I this is my weakness. Can anybody help me to make clear it? Thank you!
_________________

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Senior Manager
Joined: 29 Nov 2006
Posts: 318

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Location: Orange County, CA

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31 Jan 2008, 10:06
Quote:
Hi everybody,

I am very confused with this problem. The question is about "Amy's grade was what percentile of the grades of the two classes combined?", but guys all of you go to find the grades of not exceeding Amy's, and then credit it with what question asked. I this is my weakness. Can anybody help me to make clear it? Thank you!

The key to this question is to understand what is being asked. The question is asking where Amy's grade ranks in comparison to the two classes combined (class A: 80 kids, and class B: 100 kids). The stem gives you her ranking individually but you need to calculate her ranking overall. It's similar to a weighted average question.

Does that help?

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Re: PS: Percentile   [#permalink] 31 Jan 2008, 10:06
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