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What is the value of a ?

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What is the value of a ? [#permalink] New post 03 Apr 2013, 08:21
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A
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C
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Question Stats:

68% (01:43) correct 32% (00:36) wrong based on 56 sessions
What is the value of a ?

(1) a ^2 = b^2
(2) b − a = −12
[Reveal] Spoiler: OA

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Last edited by Bunuel on 03 Apr 2013, 08:42, edited 1 time in total.
Edited the question.
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Re: What is the value of a ? [#permalink] New post 03 Apr 2013, 08:48
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What is the value of a ?

(1) a ^2 = b^2. Clearly insufficient. But from this statement b^2-a^2=0 --> (b-a)(b+a)=0 --> b-a=0 or b+a=0.

(2) b − a = −12. Also clearly insufficient.

(1)+(2) Since from (2) b-a=-12\neq{0}, then from (1) b+a=0. So, we have two equations: b-a=-12 and b+a=0. Solving gives a=6 and b=-6. Sufficient.

Answer: C.
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Re: What is the value of a ? [#permalink] New post 03 Apr 2013, 09:01
Thanks Bunuel....your explanation is much more easier than Kaplan's...
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What is the value of a ? [#permalink] New post 09 Apr 2013, 21:26
What is the value of a ?

1.a^2 = b^2
2.b - a = -12

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Re: What is the value of a ? [#permalink] New post 09 Apr 2013, 21:37
What is the value of a ?

1.a^2 = b^2
|a|=|b| so or a=b or a=-b, we have no value of b. Not sufficient

2.b - a = -12
Clearly not sufficient.

1+2
a-b=12, so from statement 1 we can deduce that a=-b ( it cannot be a=b because a-b=b-b=0 and not 12).
-b-b=12,b=-6 and a=6. C
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Re: What is the value of a ? [#permalink] New post 09 Apr 2013, 22:24
Expert's post
subhendu009 wrote:
What is the value of a ?

1.a^2 = b^2
2.b - a = -12

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From F.S 1, we have (a-b)(a+b) = 0. Insufficient.

From F.S 2, we have b-a = -12. Insufficient.

Taking both together, we know that (a-b) is not equal to zero. Thus, (a+b) = 0, and we can get the value for a. Sufficient.

C.
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Re: What is the value of a ? [#permalink] New post 09 Apr 2013, 23:33
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Re: What is the value of a ?   [#permalink] 09 Apr 2013, 23:33
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