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

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

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24 Feb 2014, 23:58
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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.

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Math Expert
Joined: 02 Sep 2009
Posts: 60733
Re: For all numbers s and t, the operation * is defined by s*t =  [#permalink]

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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 $$-3(x+1)=-12$$ --> $$x+1=4$$ -> $$x=3$$.

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Re: For all numbers s and t, the operation * is defined by s*t =  [#permalink]

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

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

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

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26 Feb 2014, 02:13
1
Option B.
(-2)*x=-12
(-2-1)(x+1)=-12
x+1=4
x=3
Math Expert
Joined: 02 Sep 2009
Posts: 60733
Re: For all numbers s and t, the operation * is defined by s*t =  [#permalink]

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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 $$-3(x+1)=-12$$ --> $$x+1=4$$ -> $$x=3$$.

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Joined: 26 Feb 2015
Posts: 109
For all numbers s and t, the operation * is defined by s*t =  [#permalink]

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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?
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Re: For all numbers s and t, the operation * is defined by s*t =  [#permalink]

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04 Mar 2015, 00:14
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

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Math Expert
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Posts: 60733
Re: For all numbers s and t, the operation * is defined by s*t =  [#permalink]

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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
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Re: For all numbers s and t, the operation * is defined by s*t =  [#permalink]

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25 Aug 2017, 11:06
1
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

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Re: For all numbers s and t, the operation * is defined by s*t =  [#permalink]

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14 Sep 2019, 00:19
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
Re: For all numbers s and t, the operation * is defined by s*t =   [#permalink] 14 Sep 2019, 00:19
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