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What is the value of a?

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What is the value of a?  [#permalink]

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New post 31 Aug 2010, 14:46
2
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A
B
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E

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  25% (medium)

Question Stats:

69% (00:37) correct 31% (01:08) wrong based on 155 sessions

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What is the value of a?

(1) a - b + 4 = 0
(2) a = -a



Since "a" = -a, 2a = 0, or a = 0 Am I missing something here? How does 2a = 0? Confused about this one, given that a is an unknown variable. Thanks
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Re: What is the value of a?  [#permalink]

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New post 31 Aug 2010, 15:02
source?
cannt understand why 2a = 0, but my understanding is that only 0 satisfies a = -a , try plugging positive, negative and fractions in the place of a....
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New post 31 Aug 2010, 16:13
Source is the ARCO GMAT/GRE book. I don't understand how -a = 0 To me (intuitively) if a is positive, -a is negative, and if a is negative, -a is positive. Hrumphhhh!
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Re: What is the value of a?  [#permalink]

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New post 01 Sep 2010, 07:28
This question has issues, so don't spend too much time thinking about it. Zero is neither positive nor negative. I seriously doubt you would see a question on the real GMAT about positive zero vs. negative zero. GMAT tends to avoid topics that are ambiguous.
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Re: What is the value of a?  [#permalink]

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New post 01 Sep 2010, 07:40
HustleHarder wrote:
What is the value of a?

1. a - b + 4 = 0
2. a = -a



Since "a" = -a, 2a = 0, or a = 0 Am I missing something here? How does 2a = 0? Confused about this one, given that a is an unknown variable. Thanks


What is the value of a?

(1) a - b + 4 = 0 --> two variables, one equation, so we can not find uniques numerical value of \(a\). Not sufficient.

(2) a = -a --> number equals to minus itself, only number to satisfy this is zero, so \(a=0\). Sufficient.

Or: \(a=-a\) --> add \(a\) to both sides: \(a+a=-a+a\) --> \(2a=0\) --> \(a=0\).

Answer: B.


HustleHarder wrote:
Source is the ARCO GMAT/GRE book. I don't understand how -a = 0 To me (intuitively) if a is positive, -a is negative, and if a is negative, -a is positive. Hrumphhhh!


You are right "if a is positive, -a is negative, and if a is negative, -a is positive". But also if \(a=0\), then \(-a=a=0\) (0=-0).
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Re: What is the value of a?  [#permalink]

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New post 14 Aug 2017, 06:46
1st statement is definitely not sufficient.
2nd statement is sufficient if you add a to both sides. 2a=0 => a=0
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Re: What is the value of a?  [#permalink]

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New post 24 Aug 2017, 13:38
HustleHarder wrote:
What is the value of a?

(1) a - b + 4 = 0
(2) a = -a


a - b + 4 = 0

This means a = b - 4. However, since we don’t know anything about b, statement one alone is not sufficient to determine the value of a.

Statement Two Alone:

a = -a

a = -a

2a = 0

a = 0

Statement two alone is sufficient to answer the question.

Answer: B
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Re: What is the value of a?   [#permalink] 24 Aug 2017, 13:38
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