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Is a = b c? (1) c = a + b (2) a < 0

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Is a = b c? (1) c = a + b (2) a < 0 [#permalink] New post 22 Jul 2010, 12:06
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65% (01:56) correct 35% (00:55) wrong based on 70 sessions
Is ┃a┃ = b – c?

(1) c = a + b

(2) a < 0
[Reveal] Spoiler: OA

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Re: DS question [#permalink] New post 22 Jul 2010, 12:29
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aiming4mba wrote:
Is ┃a┃ = b – c?

(1) c = a + b

(2) a < 0


If a<0 it must be true that -a=b-c;
If a\geq{0} it must be true that a=b-c.

(1) c=a+b --> -a=b-c. But we don't know whether a<0. Not sufficient.
(2) a<0. Question becomes is -a=b-c? We don't know that. Not sufficient.

(1)+(2) Form 2: a<0, question becomes is -a=b-c? Statement 1 confirms this. Sufficient.

Answer: C. (similar topic: abs-equation-from-gmatprep-84821.html)
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Re: DS question [#permalink] New post 22 Jul 2010, 14:25
aiming4mba wrote:
Is ┃a┃ = b – c?

(1) c = a + b

(2) a < 0



why not (A)?

-a = b-c
therefore b-c = |a|......
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Re: DS question [#permalink] New post 22 Jul 2010, 15:06
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Quote:
why not (A)?

-a = b-c
therefore b-c = |a|......


If b-c=-a, then lal=-(b-c), or c-b=lal, which does not answer our original question, b-c=lal.

Thanks,

Jared
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Re: Is a = b c? (1) c = a + b (2) a < 0 [#permalink] New post 10 Oct 2012, 11:06
Is this approach correct?

For ┃a┃ = b – c to be true , (b - c ) >=0 ie positive

(1) c = a + b : for (b - c ) >=0 to be true a needs to be <=0. Not given, hence insufficient
(2) a < 0, says nothing about (b - c ) >=0 Hence insufficient
(1)+(2) proves b - c>=0. Sufficient.
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Re: Is a = b c? (1) c = a + b (2) a < 0 [#permalink] New post 10 Oct 2012, 22:53
I am little confused with this. The question asks is l a l = b-c, that is the question asks

Is a = b-c or a = c - b

1) c = a + b sufficiently answers this

Then why not the option A??

Bah!! no matter what I do these mods always leave me confused
Re: Is a = b c? (1) c = a + b (2) a < 0   [#permalink] 10 Oct 2012, 22:53
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