It is currently 20 Mar 2018, 05:03

### 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

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

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# For all numbers s and t, the operation * is defined by s*t =

Author Message
TAGS:

### Hide Tags

Math Expert
Joined: 02 Sep 2009
Posts: 44336
For all numbers s and t, the operation * is defined by s*t = [#permalink]

### Show Tags

24 Feb 2014, 23:58
Expert's post
3
This post was
BOOKMARKED
00:00

Difficulty:

5% (low)

Question Stats:

77% (01:04) correct 23% (01:05) wrong based on 773 sessions

### HideShow timer Statistics

The Official Guide For GMAT® Quantitative Review, 2ND Edition

For all numbers s and t, the operation * is defined by s*t = (s - 1)(t + 1). If (-2)*x = -12, then x =

(A) 2
(B) 3
(C) 5
(D) 6
(E) 11

Problem Solving
Question: 113
Category:Algebra First-degree equations
Page: 76
Difficulty: 600

GMAT Club is introducing a new project: The Official Guide For GMAT® Quantitative Review, 2ND Edition - Quantitative Questions Project

Each week we'll be posting several questions from The Official Guide For GMAT® Quantitative Review, 2ND Edition and then after couple of days we'll provide Official Answer (OA) to them along with a slution.

We'll be glad if you participate in development of this project:
2. Please vote for the best solutions by pressing Kudos button;
3. Please vote for the questions themselves by pressing Kudos button;
4. Please share your views on difficulty level of the questions, so that we have most precise evaluation.

Thank you!
[Reveal] Spoiler: OA

_________________
Math Expert
Joined: 02 Sep 2009
Posts: 44336
Re: For all numbers s and t, the operation * is defined by s*t = [#permalink]

### Show Tags

24 Feb 2014, 23:59
SOLUTION

For all numbers s and t, the operation * is defined by s*t = (s - 1)(t + 1). If (-2)*x = -12, then x =

(A) 2
(B) 3
(C) 5
(D) 6
(E) 11

Since $$s*t = (s - 1)(t + 1)$$, then $$(-2)*x = (-2-1)(x+1)=-3(x+1)$$.

So, we are given that $$-3(x+1)=-12$$ --> $$x+1=4$$ -> $$x=3$$.

_________________
Manager
Joined: 14 Jan 2013
Posts: 151
Concentration: Strategy, Technology
GMAT Date: 08-01-2013
GPA: 3.7
WE: Consulting (Consulting)
Re: For all numbers s and t, the operation * is defined by s*t = [#permalink]

### Show Tags

25 Feb 2014, 05:02
1
KUDOS
(-2)^*X= -12

= (-2-1) (X+1)= -12
x= 3

B?
_________________

"Where are my Kudos" ............ Good Question = kudos

"Start enjoying all phases" & all Sections

__________________________________________________________________
http://gmatclub.com/forum/collection-of-articles-on-critical-reasoning-159959.html

http://gmatclub.com/forum/percentages-700-800-level-questions-130588.html

http://gmatclub.com/forum/700-to-800-level-quant-question-with-detail-soluition-143321.html

Senior Manager
Joined: 20 Dec 2013
Posts: 266
Location: India
Re: For all numbers s and t, the operation * is defined by s*t = [#permalink]

### Show Tags

26 Feb 2014, 02:13
1
KUDOS
Option B.
(-2)*x=-12
(-2-1)(x+1)=-12
x+1=4
x=3
Math Expert
Joined: 02 Sep 2009
Posts: 44336
Re: For all numbers s and t, the operation * is defined by s*t = [#permalink]

### Show Tags

01 Mar 2014, 04:19
SOLUTION

For all numbers s and t, the operation * is defined by s*t = (s - 1)(t + 1). If (-2)*x = -12, then x =

(A) 2
(B) 3
(C) 5
(D) 6
(E) 11

Since $$s*t = (s - 1)(t + 1)$$, then $$(-2)*x = (-2-1)(x+1)=-3(x+1)$$.

So, we are given that $$-3(x+1)=-12$$ --> $$x+1=4$$ -> $$x=3$$.

_________________
Manager
Joined: 26 Feb 2015
Posts: 123
For all numbers s and t, the operation * is defined by s*t = [#permalink]

### Show Tags

03 Mar 2015, 14:38
Can I please get an explaination to this? Completely clueless..

How do you conclude that s = -2 and t = x?
EMPOWERgmat Instructor
Status: GMAT Assassin/Co-Founder
Affiliations: EMPOWERgmat
Joined: 19 Dec 2014
Posts: 11281
Location: United States (CA)
GMAT 1: 800 Q51 V49
GRE 1: 340 Q170 V170
Re: For all numbers s and t, the operation * is defined by s*t = [#permalink]

### Show Tags

04 Mar 2015, 00:14
Expert's post
1
This post was
BOOKMARKED
Hi erikvm,

This is an example of a "Symbolism" question (you'll likely see one of them on Test Day). The basic concept is usually pretty simple - the prompt will "make up' a math symbol, explain to you what it "means" mathematically, then ask you to use it to perform a calculation.

Since the * symbol makes people think about multiplication, I'm going to change it to a # symbol. Here, we're told....

S#T = (S-1)(T+1)

You are meant to take the numbers that S and T represent and place them into the calculation. So, as an example, if we had...

2#3 then that would equal (2-1)(3+1) = (1)(4) = 4

Knowing that, we're given....

(-2)#X = -12 and we're asked to solve for X

Let's 'substitute in' the (-2) and the X....

(-2 - 1)(X + 1) = -12

Now, you can do the algebra....
(-3)(X + 1) = -12
(X + 1) = 4
X = 3

[Reveal] Spoiler:
B

GMAT assassins aren't born, they're made,
Rich
_________________

760+: Learn What GMAT Assassins Do to Score at the Highest Levels
Contact Rich at: Rich.C@empowergmat.com

# Rich Cohen

Co-Founder & GMAT Assassin

Special Offer: Save \$75 + GMAT Club Tests Free
Official GMAT Exam Packs + 70 Pt. Improvement Guarantee
www.empowergmat.com/

***********************Select EMPOWERgmat Courses now include ALL 6 Official GMAC CATs!***********************

Math Expert
Joined: 02 Sep 2009
Posts: 44336
Re: For all numbers s and t, the operation * is defined by s*t = [#permalink]

### Show Tags

04 Mar 2015, 03:16
erikvm wrote:
Can I please get an explaination to this? Completely clueless..

How do you conclude that s = -2 and t = x?

Check other function questions in our Special Questions Directory:

Operations/functions defining algebraic/arithmetic expressions
Symbols Representing Arithmetic Operation
Rounding Functions
Various Functions
_________________
Target Test Prep Representative
Status: Founder & CEO
Affiliations: Target Test Prep
Joined: 14 Oct 2015
Posts: 2319
Location: United States (CA)
Re: For all numbers s and t, the operation * is defined by s*t = [#permalink]

### Show Tags

25 Aug 2017, 11:06
Bunuel wrote:
The Official Guide For GMAT® Quantitative Review, 2ND Edition

For all numbers s and t, the operation * is defined by s*t = (s - 1)(t + 1). If (-2)*x = -12, then x =

(A) 2
(B) 3
(C) 5
(D) 6
(E) 11

We are given that s * t = (s - 1)(t + 1).

Since (-2) * x = -12:

(-2 - 1)(x + 1) = -12

(-3)(x + 1) = -12

-3x - 3 = -12

-3x = -9

x = 3

_________________

Scott Woodbury-Stewart
Founder and CEO

GMAT Quant Self-Study Course
500+ lessons 3000+ practice problems 800+ HD solutions

Re: For all numbers s and t, the operation * is defined by s*t =   [#permalink] 25 Aug 2017, 11:06
Display posts from previous: Sort by