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

It is currently 15 Oct 2018, 06:25

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

What is the value of a ?

  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: 86
Location: Nepal
Concentration: Finance, Entrepreneurship
GPA: 3.83
WE: Accounting (Consulting)
What is the value of a ?  [#permalink]

Show Tags

New post Updated on: 03 Apr 2013, 09:42
1
00:00
A
B
C
D
E

Difficulty:

  25% (medium)

Question Stats:

73% (01:13) correct 27% (01:15) wrong based on 178 sessions

HideShow timer Statistics

What is the value of a ?

(1) a ^2 = b^2
(2) b − a = −12

_________________

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


Originally posted by atalpanditgmat on 03 Apr 2013, 09:21.
Last edited by Bunuel on 03 Apr 2013, 09:42, edited 1 time in total.
Edited the question.
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 49975
Re: What is the value of a ?  [#permalink]

Show Tags

New post 03 Apr 2013, 09:48
1
What is the value of a ?

(1) a ^2 = b^2. Clearly insufficient. But from this statement \(b^2-a^2=0\) --> \((b-a)(b+a)=0\) --> \(b-a=0\) or \(b+a=0\).

(2) b − a = −12. Also clearly insufficient.

(1)+(2) Since from (2) \(b-a=-12\neq{0}\), then from (1) \(b+a=0\). So, we have two equations: \(b-a=-12\) and \(b+a=0\). Solving gives \(a=6\) and \(b=-6\). Sufficient.

Answer: C.
_________________

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

Manager
Manager
avatar
Status: Working hard to score better on GMAT
Joined: 02 Oct 2012
Posts: 86
Location: Nepal
Concentration: Finance, Entrepreneurship
GPA: 3.83
WE: Accounting (Consulting)
Re: What is the value of a ?  [#permalink]

Show Tags

New post 03 Apr 2013, 10:01
Thanks Bunuel....your explanation is much more easier than Kaplan's...
_________________

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

VP
VP
User avatar
Status: Far, far away!
Joined: 02 Sep 2012
Posts: 1080
Location: Italy
Concentration: Finance, Entrepreneurship
GPA: 3.8
GMAT ToolKit User
Re: What is the value of a ?  [#permalink]

Show Tags

New post 09 Apr 2013, 22:37
What is the value of a ?

1\(.a^2\) = \(b^2\)
\(|a|=|b|\) so or \(a=b\) or \(a=-b\), we have no value of b. Not sufficient

2.b - a = -12
Clearly not sufficient.

1+2
\(a-b=12\), so from statement 1 we can deduce that a=-b ( it cannot be a=b because a-b=b-b=0 and not 12).
\(-b-b=12,b=-6\) and \(a=6\). C
_________________

It is beyond a doubt that all our knowledge that begins with experience.

Kant , Critique of Pure Reason

Tips and tricks: Inequalities , Mixture | Review: MGMAT workshop
Strategy: SmartGMAT v1.0 | Questions: Verbal challenge SC I-II- CR New SC set out !! , My Quant

Rules for Posting in the Verbal Forum - Rules for Posting in the Quant Forum[/size][/color][/b]

Verbal Forum Moderator
User avatar
Joined: 10 Oct 2012
Posts: 613
Premium Member
Re: What is the value of a ?  [#permalink]

Show Tags

New post 09 Apr 2013, 23:24
subhendu009 wrote:
What is the value of a ?

1\(.a^2\) = \(b^2\)
2.b - a = -12

----------------------------
Press +1 KUDOS if you like my post.


From F.S 1, we have (a-b)(a+b) = 0. Insufficient.

From F.S 2, we have b-a = -12. Insufficient.

Taking both together, we know that (a-b) is not equal to zero. Thus, (a+b) = 0, and we can get the value for a. Sufficient.

C.
_________________

All that is equal and not-Deep Dive In-equality

Hit and Trial for Integral Solutions

ISB, NUS, NTU Moderator
User avatar
G
Joined: 11 Aug 2016
Posts: 261
Reviews Badge CAT Tests
Re: What is the value of a ?  [#permalink]

Show Tags

New post 01 Sep 2018, 10:12
Harshgmat wrote:
What is the value of a ?

a) \(a^2 = b^2\)

b) b - a = -12


Statement 1: \(a^2 = b^2\)
This implies, a=+b or -b
Insufficient.

Statement 2: b - a = -12
Clearly inssuficient.

Statement 1 and 2 Together:

Case 1: a=+b
b-b=-12
0=-12
Absurd Result.

Case 2: a=-b
b+b=-12
b=-6

Hence, C is our answer.
_________________

~R.
If my post was of any help to you, You can thank me in the form of Kudos!!

GMATH Teacher
User avatar
S
Status: GMATH founder
Joined: 12 Oct 2010
Posts: 356
Re: What is the value of a ?  [#permalink]

Show Tags

New post 01 Sep 2018, 16:23
Harshgmat wrote:
What is the value of a ?

a) \(a^2 = b^2\)

b) b - a = -12


To prove that each statement alone is insufficient, we present a BIFURCATION (algebraic, in this case):

\(? = a\)

\(\left( 1 \right)\,\,{a^2} = {b^2}\)

\(Take\,\,\left\{ \begin{gathered}
{a^2} = {b^2} = 0\,\,\,\,\, \Rightarrow \,\,\,\,? = 0 \hfill \\
{a^2} = {b^2} = 1\,\,\,\,\, \Rightarrow \,\,\,\,? \ne 0\,\,\,\,\,\,\,\,\left( {a = \pm \,1} \right) \hfill \\
\end{gathered} \right.\,\,\,\,\,\,\,\,\, \Rightarrow \,\,\,\,\,\,{\text{INSUF}}{\text{.}}\)

\(\left( 2 \right)\,\,a\, - b = 12\)

\(Take\,\,\left\{ \begin{gathered}
b = 0\,\,\,\,\, \Rightarrow \,\,\,\,? = 12 \hfill \\
b = 1\,\,\,\, \Rightarrow \,\,\,\,? \ne 12\,\,\,\,\,\,\,\,\left( {a = \,13} \right) \hfill \\
\end{gathered} \right.\,\,\,\,\,\,\, \Rightarrow \,\,\,\,\,\,{\text{INSUF}}{\text{.}}\)

\(\left( {1 + 2} \right)\,\,\,\,\,\left\{ \begin{gathered}
{a^2} - {b^2} = 0\,\,\,\,\, \hfill \\
a - b = 12 \hfill \\
\end{gathered} \right. \Rightarrow \,\,\,\,\,\,\left\{ \begin{gathered}
\left( {a + b} \right)\left( {a - b} \right) = 0 \hfill \\
a - b = 12 \hfill \\
\end{gathered} \right.\,\,\,\,\,\,\,\, \Rightarrow \,\,\,\,\,\,\left\{ \begin{gathered}
a + b = 0 \hfill \\
a - b = 12 \hfill \\
\end{gathered} \right.\,\,\,\,\,\,\,\mathop \Rightarrow \limits^{\left( + \right)} \,\,\,\,\,2a = 12\,\,\,\,\,\, \Rightarrow \,\,\,\,\,a\,\,{\text{unique}} \Rightarrow \,\,\,\,\,\,{\text{SUF}}{\text{.}}\,\)


The above follows the notations and rationale taught in the GMATH method.
_________________

Fabio Skilnik :: http://www.GMATH.net (Math for the GMAT)
Course release PROMO : finish our test drive till 31/Oct with (at least) 60 correct answers out of 92 (12-questions Mock included) to gain a 60% discount!

GMAT Club Bot
Re: What is the value of a ? &nbs [#permalink] 01 Sep 2018, 16:23
Display posts from previous: Sort by

What is the value of a ?

  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®.