Find all School-related info fast with the new School-Specific MBA Forum

It is currently 23 Apr 2014, 06:35

Close

GMAT Club Daily Prep

Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track
Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

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

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:
1 KUDOS received
Intern
Intern
Joined: 16 Apr 2010
Posts: 23
Followers: 0

Kudos [?]: 1 [1] , given: 0

Amy's grade was 90th percentile of the 80 grades for her [#permalink] New post 28 Jul 2010, 08:07
1
This post received
KUDOS
00:00
A
B
C
D
E

Difficulty:

  35% (medium)

Question Stats:

64% (02:22) correct 35% (01:29) wrong based on 90 sessions
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
[Reveal] Spoiler: OA
2 KUDOS received
Math Expert
User avatar
Joined: 02 Sep 2009
Posts: 17375
Followers: 2886

Kudos [?]: 18474 [2] , given: 2357

GMAT Tests User CAT Tests
Re: Help [#permalink] New post 28 Jul 2010, 08:31
2
This post received
KUDOS
Expert's post
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

If someone's grade is in x_{th} percentile of the n grades, this means that x% of people out of n has the grades less than this person.

Being in 90th percentile out of 80 grades means Amy outscored 80*0.9=72 classmates.

In another class she would outscored 100-19=81 students (note: Amy herself is not in this class).

So, in combined classes she outscored 72+81=153. As there are total of 80+100=180 students, so Amy is in \frac{153}{180}=0.85=85%, or in 85th percentile.

Answer: D.
_________________

NEW TO MATH FORUM? PLEASE READ THIS: ALL YOU NEED FOR QUANT!!!

PLEASE READ AND FOLLOW: 11 Rules for Posting!!!

RESOURCES: [GMAT MATH BOOK]; 1. Triangles; 2. Polygons; 3. Coordinate Geometry; 4. Factorials; 5. Circles; 6. Number Theory; 7. Remainders; 8. Overlapping Sets; 9. PDF of Math Book; 10. Remainders; 11. GMAT Prep Software Analysis NEW!!!; 12. SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) NEW!!!; 12. Tricky questions from previous years. NEW!!!;

COLLECTION OF QUESTIONS:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS ; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


What are GMAT Club Tests?
25 extra-hard Quant Tests

Intern
Intern
Joined: 16 Apr 2010
Posts: 23
Followers: 0

Kudos [?]: 1 [0], given: 0

Re: Help [#permalink] New post 28 Jul 2010, 09:21
thanks for the correction and also for explanation
Manager
Manager
Joined: 24 Apr 2013
Posts: 75
Location: United States
Followers: 0

Kudos [?]: 6 [0], given: 23

Re: Amy's grade was 90th percentile of the 80 grades for her [#permalink] New post 12 Oct 2013, 04:29
I solved this question using this logic:

If there are 19 grades above Amy in the second class, and no grades are repeated, that means that Amy has the 20th highest grade which means there are 80 grades beneath her, which means that she is in the 80th percentile.

Solving using weighted average, using the number of students as weights
= [90th (80)+ 80th (100)] / 180 =85%
_________________

Struggling: make or break attempt

Intern
Intern
Joined: 02 Jul 2013
Posts: 2
Followers: 0

Kudos [?]: 0 [0], given: 1

Re: Amy's grade was 90th percentile of the 80 grades for her [#permalink] New post 13 Oct 2013, 22:05
D: 85%

I was trying to do the math quickly so I did this:

I added the percents 90%+81% = 171% then I divided it by 2 to get a estimated average of 85...

Can i do this? :shock:
Math Expert
User avatar
Joined: 02 Sep 2009
Posts: 17375
Followers: 2886

Kudos [?]: 18474 [0], given: 2357

GMAT Tests User CAT Tests
Re: Amy's grade was 90th percentile of the 80 grades for her [#permalink] New post 13 Oct 2013, 23:16
Expert's post
cowashington wrote:
D: 85%

I was trying to do the math quickly so I did this:

I added the percents 90%+81% = 171% then I divided it by 2 to get a estimated average of 85...

Can i do this? :shock:


No, you cannot. What would be your answer if one of the options were 86%? Also, if the numbers in the question were different, your approximation could give wrong answer.
_________________

NEW TO MATH FORUM? PLEASE READ THIS: ALL YOU NEED FOR QUANT!!!

PLEASE READ AND FOLLOW: 11 Rules for Posting!!!

RESOURCES: [GMAT MATH BOOK]; 1. Triangles; 2. Polygons; 3. Coordinate Geometry; 4. Factorials; 5. Circles; 6. Number Theory; 7. Remainders; 8. Overlapping Sets; 9. PDF of Math Book; 10. Remainders; 11. GMAT Prep Software Analysis NEW!!!; 12. SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) NEW!!!; 12. Tricky questions from previous years. NEW!!!;

COLLECTION OF QUESTIONS:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS ; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


What are GMAT Club Tests?
25 extra-hard Quant Tests

Intern
Intern
Joined: 29 Apr 2013
Posts: 1
Followers: 0

Kudos [?]: 0 [0], given: 2

GMAT ToolKit User
Re: Amy's grade was 90th percentile of the 80 grades for her [#permalink] New post 17 Oct 2013, 12:30
I took the following approach:

For 80 grades -> 90 percentile
For 100 grades -> 81 percentile

For 180 -> Her percentile had to be higher than 81 and lower than 90 -> The only answer satisfying this was 85% D

Please correct me if I'm wrong
Re: Amy's grade was 90th percentile of the 80 grades for her   [#permalink] 17 Oct 2013, 12:30
    Similar topics Author Replies Last post
Similar
Topics:
New posts Amy's grade was the 90th percentile of the 80 grades for her coffeeloverfreak 2 22 Sep 2005, 20:53
New posts Amy's grade was 90th percentile of the 80 grades for her X & Y 1 10 Jun 2006, 11:59
New posts Amy's grade was the 90th percentile of the 80 grades for her uphillclimb 6 16 Oct 2006, 18:42
New posts Amy's grade was the 90th percentile of the 80 grades for her chanmat 1 25 Nov 2006, 20:28
New posts 1 Amy's grade was the 90th percentile of the 80 grades for her harshavmrg 3 26 Jun 2011, 02:00
Display posts from previous: Sort by

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

  Question banks Downloads My Bookmarks Reviews Important topics  


GMAT Club MBA Forum Home| About| Privacy Policy| Terms and Conditions| GMAT Club Rules| Contact| Sitemap

Powered by phpBB © phpBB Group and phpBB SEO

Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.