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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] New post 24 Feb 2014, 22:58
Expert's post
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A
B
C
D
E

Difficulty:

  5% (low)

Question Stats:

76% (03:24) correct 24% (01:02) wrong based on 133 sessions
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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Expert Post
Math Expert
User avatar
Joined: 02 Sep 2009
Posts: 23064
Followers: 3537

Kudos [?]: 27229 [0], given: 2725

Re: For all numbers s and t, the operation * is defined by s*t = [#permalink] New post 24 Feb 2014, 22:59
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.

Answer: B.
_________________

NEW TO MATH FORUM? PLEASE READ THIS: ALL YOU NEED FOR QUANT!!!

PLEASE READ AND FOLLOW: 11 Rules for Posting!!!

RESOURCES: [GMAT MATH BOOK]; 1. Triangles; 2. Polygons; 3. Coordinate Geometry; 4. Factorials; 5. Circles; 6. Number Theory; 7. Remainders; 8. Overlapping Sets; 9. PDF of Math Book; 10. Remainders; 11. GMAT Prep Software Analysis NEW!!!; 12. SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) NEW!!!; 12. Tricky questions from previous years. NEW!!!;

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] New post 25 Feb 2014, 04:02
1
This post received
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] New post 26 Feb 2014, 01:13
1
This post received
KUDOS
Option B.
(-2)*x=-12
(-2-1)(x+1)=-12
x+1=4
x=3
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Joined: 02 Sep 2009
Posts: 23064
Followers: 3537

Kudos [?]: 27229 [0], given: 2725

Re: For all numbers s and t, the operation * is defined by s*t = [#permalink] New post 01 Mar 2014, 03:19
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.

Answer: B.
_________________

NEW TO MATH FORUM? PLEASE READ THIS: ALL YOU NEED FOR QUANT!!!

PLEASE READ AND FOLLOW: 11 Rules for Posting!!!

RESOURCES: [GMAT MATH BOOK]; 1. Triangles; 2. Polygons; 3. Coordinate Geometry; 4. Factorials; 5. Circles; 6. Number Theory; 7. Remainders; 8. Overlapping Sets; 9. PDF of Math Book; 10. Remainders; 11. GMAT Prep Software Analysis NEW!!!; 12. SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) NEW!!!; 12. Tricky questions from previous years. NEW!!!;

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.


What are GMAT Club Tests?
25 extra-hard Quant Tests

Get the best GMAT Prep Resources with GMAT Club Premium Membership

Re: For all numbers s and t, the operation * is defined by s*t =   [#permalink] 01 Mar 2014, 03:19
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