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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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New post 18 Feb 2014, 00:32
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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.
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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 18 Feb 2014, 00:47
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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

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.

Hope it's clear.

P.S. Please read and follow: rules-for-posting-please-read-this-before-posting-133935.html Pay attention to rules 2, 3, 7 and 10. Thank you.
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Joined: 29 Jan 2014
Posts: 29
GMAT 1: 510 Q36 V26
GMAT 2: 550 Q38 V28
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Kudos [?]: 2 [0], given: 52

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

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New post 18 Feb 2014, 01:23
Thanks Bunuel

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

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