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

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Intern
Joined: 29 Jan 2014
Posts: 29
GMAT 1: 510 Q36 V26
GMAT 2: 550 Q38 V28
Followers: 0

Kudos [?]: 2 [0], given: 52

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

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18 Feb 2014, 00:32
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Difficulty:

5% (low)

Question Stats:

84% (01:39) correct 16% (00:59) wrong based on 85 sessions

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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
[Reveal] Spoiler: OA

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Last edited by Bunuel on 18 Feb 2014, 00:42, edited 1 time in total.
Renamed the topic, edited the question, added the OA and moved to PS forum.
Math Expert
Joined: 02 Sep 2009
Posts: 35865
Followers: 6837

Kudos [?]: 89907 [2] , given: 10382

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

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18 Feb 2014, 00:47
2
KUDOS
Expert's post
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 $$-3(x+1)=-12$$ --> $$x+1=4$$ -> $$x=3$$.

Hope it's clear.

_________________
Intern
Joined: 29 Jan 2014
Posts: 29
GMAT 1: 510 Q36 V26
GMAT 2: 550 Q38 V28
Followers: 0

Kudos [?]: 2 [0], given: 52

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

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18 Feb 2014, 01:23
Thanks Bunuel

Will keep the rules in mind.
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Please give me Kudos if you like my post. Thank you

Re: For all numbers s and t, the operation * is defined by s*t   [#permalink] 18 Feb 2014, 01:23
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