how to calculate percentile

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thephoenix: Legendary Member; Posts: 1560; Joined: Tue Nov 17, 2009 2:38 amFollowed by: 5 members; Thanked: 137 times

by thephoenix » Tue Jan 26, 2010 9:58 am

Anne scored higher than exactly 12 of the 25 students in her class. She is in the nth percentile. What is n?

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Source: Beat The GMAT — Problem Solving | Tue Jan 26, 2010 9:58 am

ajith: Legendary Member; Posts: 1275; Joined: Thu Sep 21, 2006 11:13 pmFollowed by: 2 members; Location: Arabian Sea; Thanked: 125 times

by ajith » Tue Jan 26, 2010 10:49 am

thephoenix wrote:Anne scored higher than exactly 12 of the 25 students in her class. She is in the nth percentile. What is n?

"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". (wikipedia)

In this case percentile is 12/25*100 = 48th

Always borrow money from a pessimist, he doesn't expect to be paid back.

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kewltot: Junior | Next Rank: 30 Posts; Posts: 12; Joined: Wed Jan 20, 2010 12:02 pm; Location: california; Thanked: 2 times

by kewltot » Tue Jan 26, 2010 11:04 am

Anne scored higher than exactly 12 of the 25 students in her class. She is in the nth percentile. What is n?

Anne scored higher than exactly 12 of the 25 students in her class => she ranked 13 in the class of 25 students.

percentile = 13/25 * 100 = 52% is the right answer.

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ajith: Legendary Member; Posts: 1275; Joined: Thu Sep 21, 2006 11:13 pmFollowed by: 2 members; Location: Arabian Sea; Thanked: 125 times

by ajith » Tue Jan 26, 2010 11:18 am

kewltot wrote:Anne scored higher than exactly 12 of the 25 students in her class. She is in the nth percentile. What is n?

Anne scored higher than exactly 12 of the 25 students in her class => she ranked 13 in the class of 25 students.

percentile = 13/25 * 100 = 52% is the right answer.

If Anne's Percentile is 52 then Anne did better than 52% of the students or 13 students, which is not the case

Here Anne did better than 12 students which is 48% of the class and hence 48 percentile!

Always borrow money from a pessimist, he doesn't expect to be paid back.

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djkvakin: Senior | Next Rank: 100 Posts; Posts: 84; Joined: Sat Oct 03, 2009 1:13 pm; Thanked: 11 times

by djkvakin » Tue Jan 26, 2010 3:41 pm

Anne scored better than 12 students, and worse than exactly 12 students. This puts her in the middle of the class. Her rank is 50th percentile. Half of the class scored lower and half scored higher.

What is the correct answer?

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thephoenix: Legendary Member; Posts: 1560; Joined: Tue Nov 17, 2009 2:38 amFollowed by: 5 members; Thanked: 137 times

by thephoenix » Tue Jan 26, 2010 10:06 pm

ajith is right

percentile=(rank/strength)*100
=12/25*100=48

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