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problem solving Q

by siddhartha123 » Fri Dec 16, 2011 10:40 am
Dear all,

How to solve it ,

Amy's grade was the 90th percentile of the 80 grades for her class; of the 100 grades
from another class,19 were higher than amy's and rest were lower,if no other grade was same
as ammy's grade, then amy's was what percentile of the grades of two cases combined?

[spoiler]Ans: 85 th[/spoiler]
M.siddhartha
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by Bharath Krishnan » Fri Dec 16, 2011 11:41 am
In this question, percentile is calculated using the formula

number of candidates scored below Amy's grade
---------------------------------------------
total grades in the class

Class of 80
Amy's grade is 90th percentile of 80 grades - we do not know the number of candidates below Amy in this class.

x
--- (100) = 90.
80

Equating this we get 72.

Class of 100, there are 19 candidates who have scored more than Amy. Hence
100-19 = 81 (Amy's grade)
Number of candidates below Amy is 80.

Combining class of 80 and 100
72+80
------(100) will give 152*100/180
80+100

[spoiler]= 84.44444[/spoiler]

Ans is 85 :)

Hope this helps.
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by GMATGuruNY » Fri Dec 16, 2011 12:45 pm
siddhartha123 wrote:Dear all,

How to solve it ,

Amy's grade was the 90th percentile of the 80 grades for her class; of the 100 grades
from another class,19 were higher than amy's and rest were lower,if no other grade was same
as ammy's grade, then amy's was what percentile of the grades of two cases combined?

[spoiler]Ans: 85 th[/spoiler]
In Amy's class, the number of grades lower than Amy's = .9*80 = 72.
In the other class, since 19 of the 100 grades are higher than Amy's, the number of grades lower than Amy's = 100-19 = 81.
(Total lower than Amy's)/(Total grades) = (72+81)/(80+100) = 153/180 = 51/60 = 17/20 = 85/100 = 85%.

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by Bharath Krishnan » Fri Dec 16, 2011 11:42 pm
Oops. I was under the impression that the numerator that is to be considered as the grades lower than Amy should be a result after subtracting the higher grades from total grades; i.e 100-19=81. I chose 80 grades since it is lower than 81 and amy's grade is 81. (my understanding)

Thanks for clarifying this :)

Bharath-
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by GMATGuruNY » Sat Dec 17, 2011 3:52 am
Bharath Krishnan wrote:Oops. I was under the impression that the numerator that is to be considered as the grades lower than Amy should be a result after subtracting the higher grades from total grades; i.e 100-19=81. I chose 80 grades since it is lower than 81 and amy's grade is 81. (my understanding)

Thanks for clarifying this :)

Bharath-
Since Amy is not a member of the other class, her grade is not included among the 100 grades in the other class.
Of these 100 grades, 19 are higher than Amy's and 81 are lower.
Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
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I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.

As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.

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