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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

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

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24 Feb 2014, 23:59
Expert's post
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
KUDOS
(-2)^*X= -12

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

B?
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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
KUDOS
Option B.
(-2)*x=-12
(-2-1)(x+1)=-12
x+1=4
x=3
Math Expert
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Re: For all numbers s and t, the operation * is defined by s*t = [#permalink]

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01 Mar 2014, 04:19
Expert's post
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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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
Expert's post
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

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Math Expert
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Posts: 34091
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Kudos [?]: 76626 [0], given: 9977

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

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04 Mar 2015, 03:16
Expert's post
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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10 May 2016, 06:34
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Re: For all numbers s and t, the operation * is defined by s*t =   [#permalink] 10 May 2016, 06:34
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