GMAT Question of the Day - Daily to your Mailbox; hard ones only

It is currently 16 Jan 2019, 04:16

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.

Close

Request Expert Reply

Confirm Cancel
Events & Promotions in January
PrevNext
SuMoTuWeThFrSa
303112345
6789101112
13141516171819
20212223242526
272829303112
Open Detailed Calendar
  • The winning strategy for a high GRE score

     January 17, 2019

     January 17, 2019

     08:00 AM PST

     09:00 AM PST

    Learn the winning strategy for a high GRE score — what do people who reach a high score do differently? We're going to share insights, tips and strategies from data we've collected from over 50,000 students who used examPAL.
  • Free GMAT Strategy Webinar

     January 19, 2019

     January 19, 2019

     07:00 AM PST

     09:00 AM PST

    Aiming to score 760+? Attend this FREE session to learn how to Define your GMAT Strategy, Create your Study Plan and Master the Core Skills to excel on the GMAT.

If ax^2 + bx^3 = 5, where a and b are non-zero numbers, what

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:

Hide Tags

 
Manager
Manager
avatar
Status: Working hard to score better on GMAT
Joined: 02 Oct 2012
Posts: 83
Location: Nepal
Concentration: Finance, Entrepreneurship
GPA: 3.83
WE: Accounting (Consulting)
If ax^2 + bx^3 = 5, where a and b are non-zero numbers, what  [#permalink]

Show Tags

New post Updated on: 19 Jun 2013, 13:39
1
8
00:00
A
B
C
D
E

Difficulty:

  55% (hard)

Question Stats:

56% (01:14) correct 44% (00:57) wrong based on 250 sessions

HideShow timer Statistics

If ax^2 + bx^3 = 5, where a and b are non-zero numbers, what is the value of a + b?

(1) ax^2 = a
(2) bx^3 = b

As per the 800score, it is .

_________________

Do not forget to hit the Kudos button on your left if you find my post helpful.


Originally posted by atalpanditgmat on 14 Jun 2013, 23:57.
Last edited by Bunuel on 19 Jun 2013, 13:39, edited 3 times in total.
Edited the OA.
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 52138
Re: If ax² + bx³ = 5, where a and b are non-zero numbers, what i  [#permalink]

Show Tags

New post 15 Jun 2013, 00:19
3
The correct answer is neither C nor D. Please check OA.

If ax^2 + bx^3 = 5, where a and b are non-zero numbers, what is the value of a + b?

(1) ax^2 = a --> since \(a\) is non-zero reduce by it: \(x^2 = 1\) --> \(x = 1\) or \(x = -1\). If \(x = 1\), then \(a + b= 5\) but if \(x = -1\), then \(a - b = 5\), from which we cannot get the value of \(a+b\). Not sufficient.

(2) bx^3 = b --> since \(b\) is non-zero reduce by it: \(x^3 = 1\) --> \(x = 1\) --> \(ax^2 + bx^3 = 5\) becomes \(a + b= 5\). Sufficient.

Answer: B.
_________________

New to the Math Forum?
Please read this: Ultimate GMAT Quantitative Megathread | 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?
Extra-hard Quant Tests with Brilliant Analytics

Intern
Intern
avatar
Joined: 15 Sep 2012
Posts: 12
Re: If ax^2 + bx^3 = 5, where a and b are non-zero numbers, what  [#permalink]

Show Tags

New post 19 Jun 2013, 12:04
1
I arrived at B as well, atalpanditgmat can you please correct the OA
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 52138
Re: If ax^2 + bx^3 = 5, where a and b are non-zero numbers, what  [#permalink]

Show Tags

New post 20 Jun 2013, 00:40
Intern
Intern
avatar
Joined: 26 Oct 2014
Posts: 7
Re: If ax^2 + bx^3 = 5, where a and b are non-zero numbers, what  [#permalink]

Show Tags

New post 05 Sep 2015, 05:48
Bunuel wrote:
bugzor wrote:
I arrived at B as well, atalpanditgmat can you please correct the OA


OA edited. Thank you.


Hi,

From Statement 1 , a + b = 5 is obtained right. Why is it insufficient then? Pls help.
Math Revolution GMAT Instructor
User avatar
V
Joined: 16 Aug 2015
Posts: 6804
GMAT 1: 760 Q51 V42
GPA: 3.82
Premium Member
If ax^2 + bx^3 = 5, where a and b are non-zero numbers, what  [#permalink]

Show Tags

New post 05 Sep 2015, 21:56
Forget conventional ways of solving math questions. In DS, Variable approach is

the easiest and quickest way to find the answer without actually solving the

problem. Remember equal number of variables and equations ensures a solution.


If ax^2 + bx^3 = 5, where a and b are non-zero numbers, what is the value of a + b?

(1) ax^2 = a
(2) bx^3 = b

Transforming the original condition and the question we have 3 variables (a,b,x) and 1 equation (ax^2 + bx^3 = 5). Since we need to match the number of variables and equations,we need 2 more, therefore C is likely the answer. Using both 1) & 2) together, ax^2 + bx^3 = 5--> a+b=5 thus the answer is C. However, this is a 'trivial' case and thus is not our answer. Therefore using common mistake type 4(A),
1) ax^2=a--> x=-1,1. Substituting x=-1 to ax^2+bx^3=5 we have a-b=5 thus a=6, b=1 or a=7, b=2. Our answer is a+b=7,9..etc which is not unique and therefore not sufficient.
2) bx^3=b --> b=1, thus substituting it inside ax^2 + bx^3 = 5 gives us a+b=5. the answer is unique, therefore the answer is B.
_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only $149 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"

Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 52138
Re: If ax^2 + bx^3 = 5, where a and b are non-zero numbers, what  [#permalink]

Show Tags

New post 06 Sep 2015, 03:17
deepthij wrote:
Bunuel wrote:
bugzor wrote:
I arrived at B as well, atalpanditgmat can you please correct the OA


OA edited. Thank you.


Hi,

From Statement 1 , a + b = 5 is obtained right. Why is it insufficient then? Pls help.


From (1) we have that IF x = 1, then a + b = 5, but IF x = -1, then a - b = 5. Now, if x = -1, then from a - b = 5 we cannot say whether a + b = 5.
_________________

New to the Math Forum?
Please read this: Ultimate GMAT Quantitative Megathread | 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?
Extra-hard Quant Tests with Brilliant Analytics

Non-Human User
User avatar
Joined: 09 Sep 2013
Posts: 9406
Premium Member
Re: If ax^2 + bx^3 = 5, where a and b are non-zero numbers, what  [#permalink]

Show Tags

New post 03 Nov 2018, 07:33
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 Bot
Re: If ax^2 + bx^3 = 5, where a and b are non-zero numbers, what &nbs [#permalink] 03 Nov 2018, 07:33
Display posts from previous: Sort by

If ax^2 + bx^3 = 5, where a and b are non-zero numbers, what

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  


Copyright

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

Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne

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®.