Last visit was: 16 Jul 2024, 05:51 It is currently 16 Jul 2024, 05:51
Toolkit
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
Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

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

SORT BY:
Tags:
Show Tags
Hide Tags
Math Expert
Joined: 02 Sep 2009
Posts: 94360
Own Kudos [?]: 641261 [27]
Given Kudos: 85296
GMAT Club Legend
Joined: 19 Dec 2014
Status:GMAT Assassin/Co-Founder
Affiliations: EMPOWERgmat
Posts: 21835
Own Kudos [?]: 11783 [4]
Given Kudos: 450
Location: United States (CA)
GMAT 1: 800 Q51 V49
GRE 1: Q170 V170
Math Expert
Joined: 02 Sep 2009
Posts: 94360
Own Kudos [?]: 641261 [3]
Given Kudos: 85296
Manager
Joined: 14 Jan 2013
Posts: 114
Own Kudos [?]: 1550 [1]
Given Kudos: 30
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]
1
Kudos
(-2)^*X= -12

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

B?
Manager
Joined: 20 Dec 2013
Posts: 183
Own Kudos [?]: 291 [1]
Given Kudos: 35
Location: India
Re: For all numbers s and t, the operation * is defined by s*t = [#permalink]
1
Kudos
Option B.
(-2)*x=-12
(-2-1)(x+1)=-12
x+1=4
x=3
Manager
Joined: 26 Feb 2015
Posts: 94
Own Kudos [?]: 206 [2]
Given Kudos: 43
Re: For all numbers s and t, the operation * is defined by s*t = [#permalink]
1
Kudos
Can I please get an explaination to this? Completely clueless..

How do you conclude that s = -2 and t = x?
Target Test Prep Representative
Joined: 14 Oct 2015
Status:Founder & CEO
Affiliations: Target Test Prep
Posts: 19133
Own Kudos [?]: 22642 [1]
Given Kudos: 286
Location: United States (CA)
Re: For all numbers s and t, the operation * is defined by s*t = [#permalink]
1
Kudos
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

Math Expert
Joined: 02 Sep 2009
Posts: 94360
Own Kudos [?]: 641261 [0]
Given Kudos: 85296
Re: For all numbers s and t, the operation * is defined by s*t = [#permalink]
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 $$-3(x+1)=-12$$ --> $$x+1=4$$ -> $$x=3$$.

Math Expert
Joined: 02 Sep 2009
Posts: 94360
Own Kudos [?]: 641261 [1]
Given Kudos: 85296
Re: For all numbers s and t, the operation * is defined by s*t = [#permalink]
1
Bookmarks
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
GMAT Club Legend
Joined: 03 Jun 2019
Posts: 5283
Own Kudos [?]: 4191 [0]
Given Kudos: 160
Location: India
GMAT 1: 690 Q50 V34
WE:Engineering (Transportation)
Re: For all numbers s and t, the operation * is defined by s*t = [#permalink]
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

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!

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

s*t = (s - 1)(t + 1)
(-2)*x = -12
(-2-1)(x+1) = -12
-3x - 3 = -12
-3x = - 9
x = 3

IMO B
Tutor
Joined: 05 Apr 2011
Status:Tutor - BrushMyQuant
Posts: 1798
Own Kudos [?]: 2142 [0]
Given Kudos: 100
Location: India
Concentration: Finance, Marketing
Schools: XLRI (A)
GMAT 1: 700 Q51 V31
GPA: 3
WE:Information Technology (Computer Software)
Re: For all numbers s and t, the operation * is defined by s*t = [#permalink]
Top Contributor
Given that s*t = (s - 1)(t + 1) and (-2)*x = -12 and we need to find the value of x

To find (-2)*x we need to compare what is before and after * in (-2)*x and s*t

=> We need to substitute s with -2 and t with x in s*t = (s - 1)(t + 1) to get the value of (-2)*x

=> -2*x = (-2 - 1)(x + 1) = -3 *(x+1) = -12 (given)
=> x + 1 = $$\frac{-12}{-3}$$ = 4
=> x = 4 - 1 = 3

Hope it helps!

Watch the following video to learn the Basics of Functions and Custom Characters

Non-Human User
Joined: 09 Sep 2013
Posts: 33991
Own Kudos [?]: 851 [0]
Given Kudos: 0
Re: For all numbers s and t, the operation * is defined by s*t = [#permalink]
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.
Re: For all numbers s and t, the operation * is defined by s*t = [#permalink]
Moderator:
Math Expert
94360 posts