Percentile

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Cybermusings: Legendary Member; Posts: 559; Joined: Tue Mar 27, 2007 1:29 amFollowed by: 2 members; Thanked: 5 times

by Cybermusings » Sun Apr 29, 2007 4:04 am

Amy's grade was the 90th percentile of the 80 grades in her class. Of the grades from another class, 19 people were above Amy and the rest all below her. If no other grade was the same as Amy's grade, then Amy was what percentile of the grades of the 2 classes combines

1) 72nd
2) 80th
3) 81st
4) 85th
5) 92nd

Juvenile question - Please help me out with calculations! Are there any formulas that we can adhere to?

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jayhawk2001: Community Manager; Posts: 789; Joined: Sun Jan 28, 2007 3:51 pmFollowed by: 1 member; Location: Silicon valley, California; Thanked: 30 times

Re: Percentile

by jayhawk2001 » Sun Apr 29, 2007 8:35 am

Cybermusings wrote:Amy's grade was the 90th percentile of the 80 grades in her class. Of the grades from another class, 19 people were above Amy and the rest all below her. If no other grade was the same as Amy's grade, then Amy was what percentile of the grades of the 2 classes combines

1) 72nd
2) 80th
3) 81st
4) 85th
5) 92nd

Juvenile question - Please help me out with calculations! Are there any formulas that we can adhere to?

10% out of 80 grades are higher than Amy i.e. 8 grades
From the other class 19 people scored above Amy

So, total of 19+8 = 27 grades are higher than Amy's

Amy's combined percentile = 100 - 27/(80 + x)

Where x is the total number of grades in the other class. The
question does not mention the total number of grades in the other
class.

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Cybermusings: Legendary Member; Posts: 559; Joined: Tue Mar 27, 2007 1:29 amFollowed by: 2 members; Thanked: 5 times

by Cybermusings » Mon Apr 30, 2007 1:18 am

Oops sorry...there are a total of 100 grades in the other class...Sorry about the omission...Can you help me with percentile calculations...using some examples!

The OA btw is 85

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goutamn: Newbie | Next Rank: 10 Posts; Posts: 5; Joined: Mon Apr 30, 2007 7:14 am

by goutamn » Mon Apr 30, 2007 8:29 am

In the 1st class 10% of the class is above Amy, ie 8
& in the 2nd class 19 of 100 are above Amy. Both classes
combined 27 ppl are above Amy. % above Amy in both classes
combined is 27/180 = 15 % That slots Amy in the (100-1) = 85th percentile

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jayhawk2001: Community Manager; Posts: 789; Joined: Sun Jan 28, 2007 3:51 pmFollowed by: 1 member; Location: Silicon valley, California; Thanked: 30 times

by jayhawk2001 » Mon Apr 30, 2007 9:00 pm

Cybermusings wrote:Oops sorry...there are a total of 100 grades in the other class...Sorry about the omission...Can you help me with percentile calculations...using some examples!

The OA btw is 85

Assume there are 5 people in a class and they get the following scores
out of 100.

60 70 80 90 100

The person getting 90 has a "percentage" score of 90. But only 1
person has a higher score than him. So, he falls in the upper 1 / 5
of the class. Translating this to percentile, (1 - 1/5)*100 = 80 percentile
i.e. 80% of the class is below what he has scored.

Using this for the question in hand,

Total of 19+8 = 27 grades are higher than Amy's

Amy's combined percentile = 1 - 27/(80 + 100) = 85 percentile

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Scott@TargetTestPrep: GMAT Instructor; Posts: 8177; Joined: Sat Apr 25, 2015 10:56 amFollowed by: 29 members; Location: Los Angeles, CA; Thanked: 43 times

by Scott@TargetTestPrep » Mon May 20, 2019 6:14 pm

Cybermusings wrote:Amy's grade was the 90th percentile of the 80 grades in her class. Of the grades from another class, 19 people were above Amy and the rest all below her. If no other grade was the same as Amy's grade, then Amy was what percentile of the grades of the 2 classes combines

1) 72nd
2) 80th
3) 81st
4) 85th
5) 92nd

Since Amy's grade is in the 90th percentile of the 80 grades in her class, 10% of the number of total grades in her class are not lower than Amy's grade; i.e., 8 grades. Note that these 8 grades include Amy's own grade. When combined with the number of grades from the other class, there are 8 + 19 = 27 grades that are not lower than Amy's grade, including Amy's own, in a total of 80 + 100 = 180 grades. Since 27 / 180 = 0.15, this amounts to 15% of all the grades. Therefore, Amy's grade is the 100 - 15 = 85th percentile of the combined grades of the two classes.

Answer: D

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