Author 
Message 
TAGS:

Hide Tags

Intern
Joined: 20 Oct 2010
Posts: 10

Angela’s grade was in the 90th percentile out of 80 grades [#permalink]
Show Tags
09 Dec 2010, 08:22
2
This post received KUDOS
12
This post was BOOKMARKED
Question Stats:
73% (02:28) correct
27% (01:38) wrong based on 360 sessions
HideShow timer Statistics
Angela’s grade was in the 90th percentile out of 80 grades in her class. In another class of 100 students there were 19 grades higher than Angela’s. If nobody had Angela’s grade, then Angela was what percentile of the two classes combined? A. 72 B. 80 C. 81 D. 85 E. 92
Official Answer and Stats are available only to registered users. Register/ Login.
Last edited by Bunuel on 10 Jun 2013, 04:04, edited 2 times in total.
Edited the stem.



Math Expert
Joined: 02 Sep 2009
Posts: 39753

Re: Some PS problems Part 2 [#permalink]
Show Tags
09 Dec 2010, 08:33
1
This post received KUDOS
Expert's post
6
This post was BOOKMARKED
gdk800 wrote: Angela’s grade was in the 90th percentile out of 80 grades in her class. In another class of 100 students there were 19 grades higher than Angela’s. If nobody had Angela’s grade, then Angela was what percentile of the two classes combined?
a. 72 b. 80 c. 81 d. 85 e. 92 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 Angela outscored \(80*0.9=72\) classmates. In another class she would outscored \(10019=81\) students (note: Angela 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 Angela is in \(\frac{153}{180}=0.85=85%\), or in 85th percentile. Answer: D.
_________________
New to the Math Forum? Please read this: All You Need for Quant  PLEASE READ AND FOLLOW: 12 Rules for Posting!!! Resources: GMAT Math Book  Triangles  Polygons  Coordinate Geometry  Factorials  Circles  Number Theory  Remainders; 8. Overlapping Sets  PDF of Math Book; 10. Remainders  GMAT Prep Software Analysis  SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS)  Tricky questions from previous years.
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? Extrahard Quant Tests with Brilliant Analytics



Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 7449
Location: Pune, India

Re: Some PS problems Part 2 [#permalink]
Show Tags
09 Dec 2010, 13:56
5
This post received KUDOS
Expert's post
2
This post was BOOKMARKED
gdk800 wrote: Angela’s grade was in the 90th percentile out of 80 grades in her class. In another class of 100 students there were 19 grades higher than Angela’s. If nobody had Angela’s grade, then Angela was what percentile of the two classes combined?
a. 72 b. 80 c. 81 d. 85 e. 92 She is in 90th percentile in one class and 81st in the other. We need to find her 'average percentile'. The average will lie between 81 and 90 so it has to be 85! If we had closer answer options e.g. 84, 86 etc, we would need to calculate the weighted average. Using weights as 80 and 100 respectively, you can find their average using weighted average formula which is as given below: \(C_{avg} = \frac{C_1*W_1 + C_2 * W_2}{W_1 + W_2}\) \(C_{avg} = \frac{90*80 + 81*100}{180}\) = 85 In case you are not comfortable with weighted averages, check this discussion: http://gmatclub.com/forum/toughds105651.html#p828579and get back if there is a doubt.
_________________
Karishma Veritas Prep  GMAT Instructor My Blog
Get started with Veritas Prep GMAT On Demand for $199
Veritas Prep Reviews



Manager
Joined: 13 Jul 2010
Posts: 167

Re: Some PS problems Part 2 [#permalink]
Show Tags
09 Dec 2010, 19:55
Thanks Karishma, I put it to good use on this question. To all, the discussion in the link Karishma provided is very helpful.



Intern
Joined: 20 Oct 2010
Posts: 10

Re: Some PS problems Part 2 [#permalink]
Show Tags
10 Dec 2010, 11:57
Thanx a ton to Bunuel & Karishma for such detailed explanations.
Special thanx to Bunuel for editing the question part i missed n also to Karishma for the helpful link on weighted averages.



Senior Manager
Status: Bring the Rain
Joined: 17 Aug 2010
Posts: 400
Location: United States (MD)
Concentration: Strategy, Marketing
Schools: Michigan (Ross)  Class of 2014
GPA: 3.13
WE: Corporate Finance (Aerospace and Defense)

Re: Some PS problems Part 2 [#permalink]
Show Tags
10 Dec 2010, 17:45
VeritasPrepKarishma wrote: gdk800 wrote: Angela’s grade was in the 90th percentile out of 80 grades in her class. In another class of 100 students there were 19 grades higher than Angela’s. If nobody had Angela’s grade, then Angela was what percentile of the two classes combined?
a. 72 b. 80 c. 81 d. 85 e. 92 She is in 90th percentile in one class and 81st in the other. We need to find her 'average percentile'. The average will lie between 81 and 90 so it has to be 85! If we had closer answer options e.g. 84, 86 etc, we would need to calculate the weighted average. Using weights as 80 and 100 respectively, you can find their average using weighted average formula which is as given below: \(C_{avg} = \frac{C_1*W_1 + C_2 * W_2}{W_1 + W_2}\) \(C_{avg} = \frac{90*80 + 81*100}{180}\) = 85 In case you are not comfortable with weighted averages, check this discussion: http://gmatclub.com/forum/toughds105651.html#p828579and get back if there is a doubt. This formula helped tremendously. Thanks
_________________
Go Blue!
GMAT Club Premium Membership  big benefits and savings



Math Expert
Joined: 02 Sep 2009
Posts: 39753

Re: Angela’s grade was in the 90th percentile out of 80 grades [#permalink]
Show Tags
10 Jun 2013, 05:09



Intern
Joined: 09 Apr 2013
Posts: 32
Location: United States
Concentration: Social Entrepreneurship, Strategy
GPA: 3.55

Re: Angela’s grade was in the 90th percentile out of 80 grades [#permalink]
Show Tags
10 Jun 2013, 07:26
1
This post received KUDOS
gdk800 wrote: Angela’s grade was in the 90th percentile out of 80 grades in her class. In another class of 100 students there were 19 grades higher than Angela’s. If nobody had Angela’s grade, then Angela was what percentile of the two classes combined?
A. 72 B. 80 C. 81 D. 85 E. 92 Angela is 90th percentile in her class and would be 81st percentile in the other class. The ratio of her class size to the ratio of the other class size is 80:100 or 4:5. Because of that, we know that her congregate percentile is weighted more heavily towards the 81st percentile because there are more students in the class, at the same ratio as the class size. Draw a number line between 81 and 90 and apply the reverse of the class size ratio to account for the weight of each individual percentile. Thus, the congregate percentile is 4 away from 81 and 5 away from 90 818590 Answer is D



Manager
Joined: 07 Dec 2009
Posts: 108
GMAT Date: 12032014

Re: Angela’s grade was in the 90th percentile out of 80 grades [#permalink]
Show Tags
13 Jul 2014, 11:34
90th Percentile means she has scored more then 90% of the people. ==> (90/100)*80 = 72 ( she scored more then 72 people)
In the other class of 100, we are given that 19 people scored more then Angela ==> 100  19 = 81 ( she scored more then 81 people)
Since we are told to find her percentile in the combined class, we need to find how many people did she score over in a combined class of 100 + 80 = 180.
(81+72)/180 = 85 %
Answer is D.
One could also use the logic that if in the first class her percentile was 90 and in the second her percentile was 81, the average would be greater then 81 and less than 90. Hence the Answer has to be D



GMAT Club Legend
Joined: 09 Sep 2013
Posts: 16026

Re: Angela’s grade was in the 90th percentile out of 80 grades [#permalink]
Show Tags
10 Aug 2015, 05:55
Hello from the GMAT Club BumpBot! Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up  doing my job. I think you may find it valuable (esp those replies with Kudos). Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________
GMAT Books  GMAT Club Tests  Best Prices on GMAT Courses  GMAT Mobile App  Math Resources  Verbal Resources



GMAT Club Legend
Joined: 09 Sep 2013
Posts: 16026

Re: Angela’s grade was in the 90th percentile out of 80 grades [#permalink]
Show Tags
17 Nov 2016, 06:08
Hello from the GMAT Club BumpBot! Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up  doing my job. I think you may find it valuable (esp those replies with Kudos). Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________
GMAT Books  GMAT Club Tests  Best Prices on GMAT Courses  GMAT Mobile App  Math Resources  Verbal Resources



BSchool Forum Moderator
Joined: 12 Aug 2015
Posts: 2185

Re: Angela’s grade was in the 90th percentile out of 80 grades [#permalink]
Show Tags
14 Dec 2016, 15:33
1
This post was BOOKMARKED
Nice Question => Here is what i did in this one => Number of students in class 1 with score greater than angela => 10/100 *80=> 8 Number if students in class with score greater than angela => 19
Total students with score >angela => 19+8=27 Combined class strength = 100+80=180 27 is 15 percent of 180
Hence 85 percent scored less than angela. In other words => Angela's Rank would be 85 percentile
Hence D
_________________
Give me a hell yeah ...!!!!!




Re: Angela’s grade was in the 90th percentile out of 80 grades
[#permalink]
14 Dec 2016, 15:33







