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

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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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New post 25 Feb 2014, 04:02
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(-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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New post 26 Feb 2014, 01:13
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Option B.
(-2)*x=-12
(-2-1)(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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For all numbers s and t, the operation * is defined by s*t = [#permalink]

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New post 03 Mar 2015, 13:38
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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New post 03 Mar 2015, 23:14
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

Final Answer:
[Reveal] Spoiler:
B


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

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New post 04 Mar 2015, 02:16
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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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.


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

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Re: For all numbers s and t, the operation * is defined by s*t =   [#permalink] 10 May 2016, 05:34
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