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

It is currently 10 Jul 2014, 20:38

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

What is the ratio of r to s?

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:
Manager
Manager
avatar
Joined: 10 Feb 2011
Posts: 116
Followers: 1

Kudos [?]: 18 [0], given: 10

What is the ratio of r to s? [#permalink] New post 15 Mar 2011, 15:48
2
This post was
BOOKMARKED
00:00
A
B
C
D
E

Difficulty:

  25% (low)

Question Stats:

69% (01:40) correct 30% (00:40) wrong based on 133 sessions
What is the ratio of r to s?

(1) r + s = 7
(2) r^2 – s^2 = 7
[Reveal] Spoiler: OA

Last edited by Bunuel on 29 Jul 2013, 07:29, edited 1 time in total.
Edited the question.
Director
Director
avatar
Joined: 01 Feb 2011
Posts: 771
Followers: 14

Kudos [?]: 79 [0], given: 42

GMAT Tests User
Re: 20. (M) What is the ratio of r to s? (1) r + s = 7 (2) r2 [#permalink] New post 16 Mar 2011, 15:36
1. Not sufficient

(r , s could be 5 2 or 4 3 so on)

2. Not enough info to derive r/s . Not sufficient.

Together its sufficient to find r and s. Answer C.
Intern
Intern
avatar
Joined: 12 Oct 2011
Posts: 6
Location: Canada
Concentration: Finance, Entrepreneurship
GMAT 1: Q V0
WE: Asset Management (Mutual Funds and Brokerage)
Followers: 0

Kudos [?]: 5 [0], given: 4

Re: (M) What is the ratio of r to s? (1) r + s = 7 (2) r2 s2 = 7 [#permalink] New post 29 Jul 2013, 07:27
For (2), I did the following:

r^2 - s^2 = 7
(r+s)(r-s) = 7
(4+3)(4-3) = 7 <--- I don't see any other possible combination of numbers that would give you 7

Thus, I fail to see how statement 2 is insufficient. Please help!
Expert Post
1 KUDOS received
Math Expert
User avatar
Joined: 02 Sep 2009
Posts: 18492
Followers: 3187

Kudos [?]: 21207 [1] , given: 2537

Re: (M) What is the ratio of r to s? (1) r + s = 7 (2) r2 s2 = 7 [#permalink] New post 29 Jul 2013, 07:32
1
This post received
KUDOS
Expert's post
Startup wrote:
What is the ratio of r to s?

(1) r + s = 7
(2) r^2 – s^2 = 7


For (2), I did the following:

r^2 - s^2 = 7
(r+s)(r-s) = 7
(4+3)(4-3) = 7 <--- I don't see any other possible combination of numbers that would give you 7

Thus, I fail to see how statement 2 is insufficient. Please help!


Notice that we are not told that r and s are integers, so consider r^2=7 and s=0 OR r^2=8 and s=1...
_________________

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

Intern
Intern
avatar
Joined: 18 May 2013
Posts: 41
Concentration: Real Estate, Finance
GMAT 1: 660 Q V
GPA: 3.73
WE: Analyst (Real Estate)
Followers: 0

Kudos [?]: 3 [0], given: 2

Re: What is the ratio of r to s? [#permalink] New post 15 Sep 2013, 22:14
Why can't R+S = 7 be solved to (-7/1) = (-S/R) and thus prove sufficiency in Statement 1?
Expert Post
Math Expert
User avatar
Joined: 02 Sep 2009
Posts: 18492
Followers: 3187

Kudos [?]: 21207 [0], given: 2537

Re: What is the ratio of r to s? [#permalink] New post 16 Sep 2013, 01:07
Expert's post
stevennu wrote:
Why can't R+S = 7 be solved to (-7/1) = (-S/R) and thus prove sufficiency in Statement 1?


First of all: when a DS question asks about the value, then the statement is sufficient ONLY if you can get the single numerical value.

From r + s = 7 we cannot find the single numerical value of r/s, it can take infinitely many values:
...
r=-1 and s=8 --> r/s=-1/8;
r=1 and s=6 --> r/s=1/6;
r=2 and s=5 --> r/s=2/5;
...

Also notice that your example does not satisfy the equation at all: if r=1 and s=-7, then r + s = -6 not 7.

Hope this helps.
_________________

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

Intern
Intern
avatar
Joined: 17 Jun 2013
Posts: 15
Followers: 0

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

Re: What is the ratio of r to s? [#permalink] New post 16 Sep 2013, 19:13
I stumbled upon C) to be the right answer but I'm not quite sure how...
1) r+s=7
2)r^2 - s^2 = 7
(r+s)(r-s)=7
r-s=1

Is the question not asking for r/s = ?
Expert Post
Math Expert
User avatar
Joined: 02 Sep 2009
Posts: 18492
Followers: 3187

Kudos [?]: 21207 [0], given: 2537

Re: What is the ratio of r to s? [#permalink] New post 16 Sep 2013, 23:34
Expert's post
Ksterr wrote:
I stumbled upon C) to be the right answer but I'm not quite sure how...
1) r+s=7
2)r^2 - s^2 = 7
(r+s)(r-s)=7
r-s=1

Is the question not asking for r/s = ?


What is the ratio of r to s?

Questions asks to find the value of r/s.

(1) r + s = 7. Infinite pairs of (r, s) satisfies this equations. Not sufficient.

(2) r^2 – s^2 = 7. Infinite pairs of (r, s) satisfies this equations. Not sufficient.

(1)+(2) From (2) we know that (r - s)(r + s) = 7, since from (1) r + s = 7, then (r - s)*7 = 7, which gives r - s = 1. Solving r + s = 7 and r - s = 1 gives r = 4 and s = 3 --> r/s = 4/3. Sufficient.

Answer: C.

Hope it's clear.
_________________

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

Intern
Intern
avatar
Joined: 13 Mar 2014
Posts: 2
Followers: 0

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

Manhattan GMAT CAT Question [#permalink] New post 20 May 2014, 20:00
I came across a question in one of my CAT practice exams and I thought I answered it correctly, but it turns out I was wrong. But I have no idea why my solution is not valid as I get the same answer as the solutions manual (just with a different approach). Can someone clarify this for me?

Thank you!

What is the ratio of r to s?

(1) r + s = 7

(2) r^2 – s^2 = 7

I answered (B) - statement 2 is sufficient. My reasoning was:

Numbers: 1, 2, 3, 4, 5, 6 etc
Their perfect square: 1, 4, 9, 16, 25 etc.
There is only one occasion in which the difference between two squared numbers is 7 and this 16-9 or 4^2 - 3^2. Thus the ratio of r/s would be 4/3.
Even if you use -1, -2, -3, -4, -5, -6 etc it makes no difference because you still get 4/3.

The solution states that you need both (answer C) in order to solve the problem (and they come up with 4/3 as well). Now using both statements is perfectly valid but why can't I get away with using only (2)?

Any help would be much appreciated!
1 KUDOS received
Moderator
Moderator
User avatar
Joined: 25 Apr 2012
Posts: 508
Location: India
Concentration: Marketing, International Business
GPA: 3.21
WE: Business Development (Other)
Followers: 11

Kudos [?]: 196 [1] , given: 552

Re: Manhattan GMAT CAT Question [#permalink] New post 20 May 2014, 20:56
1
This post received
KUDOS
zsoltvigh wrote:
I came across a question in one of my CAT practice exams and I thought I answered it correctly, but it turns out I was wrong. But I have no idea why my solution is not valid as I get the same answer as the solutions manual (just with a different approach). Can someone clarify this for me?

Thank you!

What is the ratio of r to s?

(1) r + s = 7

(2) r^2 – s^2 = 7

I answered (B) - statement 2 is sufficient. My reasoning was:

Numbers: 1, 2, 3, 4, 5, 6 etc
Their perfect square: 1, 4, 9, 16, 25 etc.
There is only one occasion in which the difference between two squared numbers is 7 and this 16-9 or 4^2 - 3^2. Thus the ratio of r/s would be 4/3.
Even if you use -1, -2, -3, -4, -5, -6 etc it makes no difference because you still get 4/3.

The solution states that you need both (answer C) in order to solve the problem (and they come up with 4/3 as well). Now using both statements is perfectly valid but why can't I get away with using only (2)?

Any help would be much appreciated!


Hello zsoltvigh,

Welcome to Gmatclub..

The Question is discussed here : what-is-the-ratio-of-r-to-s-110947.html#p1267783
As you scroll through the posts in the above link you will find the answer as C and not B....(Hint consider a case where s=0....and see what you get as ratio r/s what-is-the-ratio-of-r-to-s-110947.html#p1251159)

Note that when you have some doubts on questions especially from MGMAT Test or Veritas prep test, use the search option to check if the question has been discussed before.It will get you answers faster than waiting for response.....

If you don't find you are more than welcome to post it on the Forum
_________________


“If you can't fly then run, if you can't run then walk, if you can't walk then crawl, but whatever you do you have to keep moving forward.”

Manager
Manager
User avatar
Joined: 20 Dec 2013
Posts: 107
Followers: 1

Kudos [?]: 37 [0], given: 1

Re: What is the ratio of r to s? [#permalink] New post 20 May 2014, 21:11
banksy wrote:
What is the ratio of r to s?

(1) r + s = 7
(2) r^2 – s^2 = 7


Statement I is insufficient:

r = 2, s = 5
r = 1, s = 6

Statement II is insufficient:
(r+s)(r-s) = 7
r = 4, s = 3
r = -4, s = 3

Combining is sufficient:
r + s = 7
(r+s) (r-s) = 7
r - s = 1, r + s = 7
We get definite values of r and s hence answer is C.
_________________

Perfect Scores

If you think our post was valuable then please encourage us with Kudos :)

To learn GMAT for free visit:

http://Perfect-Scores.com
http://Youtube.com/PerfectScores
http://Facebook.com/PerfectScores

Intern
Intern
avatar
Joined: 25 Mar 2014
Posts: 4
WE: Information Technology (Computer Software)
Followers: 0

Kudos [?]: 1 [0], given: 12

Re: What is the ratio of r to s? [#permalink] New post 20 May 2014, 22:39
It's better to use algerabic forumale rather than picking numbers as the exponent is 2.

Also R power 2 - S power 2 can be written as (R+S)(R-S).

I used statement 1 to deduct R-S.

Then Combine Statement1 and R-S to get the value of R.

Obviously we will get S value from any statement. No need to calculate as its a DS q.

I might belong to that band which assumes given variables are integers though it's not explicitly given.

Kudos!
Expert Post
Math Expert
User avatar
Joined: 02 Sep 2009
Posts: 18492
Followers: 3187

Kudos [?]: 21207 [0], given: 2537

Re: Manhattan GMAT CAT Question [#permalink] New post 21 May 2014, 00:41
Expert's post
zsoltvigh wrote:
I came across a question in one of my CAT practice exams and I thought I answered it correctly, but it turns out I was wrong. But I have no idea why my solution is not valid as I get the same answer as the solutions manual (just with a different approach). Can someone clarify this for me?

Thank you!

What is the ratio of r to s?

(1) r + s = 7

(2) r^2 – s^2 = 7

I answered (B) - statement 2 is sufficient. My reasoning was:

Numbers: 1, 2, 3, 4, 5, 6 etc
Their perfect square: 1, 4, 9, 16, 25 etc.
There is only one occasion in which the difference between two squared numbers is 7 and this 16-9 or 4^2 - 3^2. Thus the ratio of r/s would be 4/3.
Even if you use -1, -2, -3, -4, -5, -6 etc it makes no difference because you still get 4/3.

The solution states that you need both (answer C) in order to solve the problem (and they come up with 4/3 as well). Now using both statements is perfectly valid but why can't I get away with using only (2)?

Any help would be much appreciated!


Merging similar topics. Please refer to the discussion above.

P.S. please read carefully and follow: rules-for-posting-please-read-this-before-posting-133935.html Pay attention to rules 1, 2, and 3. Thank you.
_________________

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: Manhattan GMAT CAT Question   [#permalink] 21 May 2014, 00:41
    Similar topics Author Replies Last post
Similar
Topics:
Experts publish their posts in the topic If p/3 = r/2 and r = 0.75s, what is the ratio of p to r to s mattce 1 07 Jul 2013, 20:59
If r and s are positive integers and the ratio of r/s is aaron22197 1 12 Jun 2008, 02:43
6r-9s/r-s then what is the ratio of r to s A) 6:1 B) 5:2 C) Capthan 1 08 Mar 2008, 06:13
If R and S are positive integers and ratio of r/s is nfa1rhp 2 21 Jul 2007, 10:19
If R and S are positive integers and the ratio of r/s is desiguy 3 29 Oct 2005, 09:10
Display posts from previous: Sort by

What is the ratio of r to s?

  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®.