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

It is currently 20 Aug 2014, 05:04

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

If x, y and k are positive numbers such that

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:
Senior Manager
Senior Manager
User avatar
Joined: 18 Aug 2009
Posts: 305
Followers: 3

Kudos [?]: 82 [0], given: 9

GMAT Tests User
If x, y and k are positive numbers such that [#permalink] New post 01 Nov 2009, 20:01
00:00
A
B
C
D
E

Difficulty:

  45% (medium)

Question Stats:

50% (02:05) correct 50% (01:20) wrong based on 82 sessions
If x, y and k are positive numbers such that

[x/(x+y)](10)+[y/(x+y)](20)=k and if x < y,

which of the following could be the value of k?

(A) 10
(B) 12
(C) 15
(D) 18
(E) 30

Open discussion of this question is here: if-x-y-and-k-are-positive-numbers-such-that-x-x-y-128231.html
[Reveal] Spoiler: OA

Last edited by Bunuel on 27 Apr 2012, 21:30, edited 1 time in total.
Topic is locked
Kaplan Promo CodeKnewton GMAT Discount CodesVeritas Prep GMAT Discount Codes
Expert Post
1 KUDOS received
Math Expert
User avatar
Joined: 02 Sep 2009
Posts: 19027
Followers: 3360

Kudos [?]: 24351 [1] , given: 2677

Re: which could be the value of K? [#permalink] New post 01 Nov 2009, 20:11
1
This post received
KUDOS
Expert's post
10*\frac{x+2y}{x+y}=k

10*(\frac{x+y}{x+y}+\frac{y}{x+y})=k

Finally we get: 10*(1+\frac{y}{x+y})=k


We know that x<y

Hence \frac{y}{x+y} is more than 0.5 and less than 1

0.5<\frac{y}{x+y}<1

So, 15<10*(1+\frac{y}{x+y})<20


Only answer between 15 and 20 is 18.

Answer: D (18)

This question was discussed before, please refer to the other approaches at: what-is-the-value-of-k-85382.html#p640124
_________________

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

Get the best GMAT Prep Resources with GMAT Club Premium Membership

Senior Manager
Senior Manager
User avatar
Joined: 18 Aug 2009
Posts: 305
Followers: 3

Kudos [?]: 82 [0], given: 9

GMAT Tests User
Re: which could be the value of K? [#permalink] New post 01 Nov 2009, 20:29
Bunuel wrote:
10*\frac{x+2y}{x+y}=k

10*(\frac{x+y}{x+y}+\frac{y}{x+y})=k

Finally we get: 10*(1+\frac{y}{x+y})=k


We know that x<y

Hence \frac{y}{x+y} is more than 0.5 and less than 1

0.5<\frac{y}{x+y}<1

So, 15<10*(1+\frac{y}{x+y})<20


Only answer between 15 and 20 is 18.

Answer: D (18)

This question was discussed before, please refer to the other approaches at: what-is-the-value-of-k-85382.html#p640124


Thanks for the solution and the pointer to the earlier thread.
I'd run a search but didn't hit that thread... maybe due to the mathematical formula.

hit a roadblock right in the first step of simplifying the equation... 10(x+2y)/(x+y)
But now understood the approach :(
SVP
SVP
avatar
Joined: 16 Nov 2010
Posts: 1692
Location: United States (IN)
Concentration: Strategy, Technology
Followers: 30

Kudos [?]: 285 [0], given: 36

GMAT Tests User Premium Member Reviews Badge
Re: which could be the value of K? [#permalink] New post 09 May 2011, 04:13
Let us try x = 1, y = 4

=> 1/5 * 10 + 4/5 * 20 = k

=> 2 + 16 = k

=> k = 18


Answer - D
_________________

Formula of Life -> Achievement/Potential = k * Happiness (where k is a constant)

Get the best GMAT Prep Resources with GMAT Club Premium Membership

2 KUDOS received
Manager
Manager
avatar
Status: Do till 740 :)
Joined: 13 Jun 2011
Posts: 103
Concentration: Strategy, General Management
GMAT 1: 460 Q35 V20
GPA: 3.6
WE: Consulting (Computer Software)
Followers: 0

Kudos [?]: 5 [2] , given: 18

GMAT ToolKit User
Re: which could be the value of K? [#permalink] New post 27 Apr 2012, 18:46
2
This post received
KUDOS
Hi Bunuel,

Is this approach ok?
since it is of the weighted averages form


10x + 20 y/x+y= k

and 20 pulls the averagge more twds itself we can eliminate other options and oly 18 wud be possible?
Expert Post
Math Expert
User avatar
Joined: 02 Sep 2009
Posts: 19027
Followers: 3360

Kudos [?]: 24351 [0], given: 2677

Re: which could be the value of K? [#permalink] New post 27 Apr 2012, 21:28
Expert's post
shankar245 wrote:
Hi Bunuel,

Is this approach ok?
since it is of the weighted averages form


10x + 20 y/x+y= k

and 20 pulls the averagge more twds itself we can eliminate other options and oly 18 wud be possible?


Yes, you can use weighted average approach for this question:

We have: \frac{10x+20y}{x+y}=k, if you look at this equation you'll notice that it's a weighted average.

There are x red boxes and y blue boxes. Red box weight is 10kg and blue box weight 20kg, what is the average weight of x red boxes and y blue boxes?

k represents the weighted average. As y>x, then the weighted average k, must be closer to 20 than to 10. 18 is the only choice satisfying this condition.

Answer: D.

In case of any question please post it here: if-x-y-and-k-are-positive-numbers-such-that-x-x-y-128231.html
_________________

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

Get the best GMAT Prep Resources with GMAT Club Premium Membership

Re: which could be the value of K?   [#permalink] 27 Apr 2012, 21:28
    Similar topics Author Replies Last post
Similar
Topics:
5 Experts publish their posts in the topic If x, y, and k are positive numbers such that eresh 31 15 Oct 2009, 15:08
If x, y, and k are positive numbers such that (10) + (20) = suntaurian 2 09 Feb 2008, 15:05
Experts publish their posts in the topic If x, y, and k are positive numbers such that marcodonzelli 3 05 Jan 2008, 12:13
If x, y, and k are positive numbers such that lan583 8 19 Nov 2006, 13:13
If x, y, and k are positive numbers such that : (10) + Antmavel 4 16 Oct 2004, 06:03
Display posts from previous: Sort by

If x, y and k are positive numbers such that

  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®.