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# What is the value of a?

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Intern
Joined: 20 Apr 2010
Posts: 31
What is the value of a? [#permalink]

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31 Aug 2010, 14:46
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Difficulty:

25% (medium)

Question Stats:

64% (00:26) correct 36% (00:47) wrong based on 152 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
Manager
Joined: 16 Feb 2010
Posts: 190
Re: What is the value of a? [#permalink]

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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....
Intern
Joined: 20 Apr 2010
Posts: 31
Re: What is the value of a? [#permalink]

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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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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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Joined: 02 Sep 2009
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Re: What is the value of a? [#permalink]

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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: $$a+a=-a+a$$ --> $$2a=0$$ --> $$a=0$$.

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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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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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.

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

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