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# What is the value of a?

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Intern
Joined: 20 Apr 2010
Posts: 36

Kudos [?]: 3 [1], given: 7

What is the value of a? [#permalink]

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31 Aug 2010, 13:46
1
KUDOS
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Difficulty:

15% (low)

Question Stats:

64% (00:27) correct 36% (00:47) wrong based on 150 sessions

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What is the value of a?

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

[Reveal] Spoiler:
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
[Reveal] Spoiler: OA

Kudos [?]: 3 [1], given: 7

Manager
Joined: 16 Feb 2010
Posts: 217

Kudos [?]: 398 [0], given: 16

Re: What is the value of a? [#permalink]

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31 Aug 2010, 14:02
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....

Kudos [?]: 398 [0], given: 16

Intern
Joined: 20 Apr 2010
Posts: 36

Kudos [?]: 3 [0], given: 7

Re: What is the value of a? [#permalink]

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31 Aug 2010, 15:13
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!

Kudos [?]: 3 [0], given: 7

Joined: 31 Dec 1969

Kudos [?]: [0], given:

Location: Russian Federation
GMAT 3: 740 Q40 V50
GMAT 4: 700 Q48 V38
GMAT 5: 710 Q45 V41
GMAT 6: 680 Q47 V36
GMAT 9: 740 Q49 V42
GMAT 11: 500 Q47 V33
GMAT 14: 760 Q49 V44
WE: Supply Chain Management (Energy and Utilities)
Re: What is the value of a? [#permalink]

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01 Sep 2010, 06:28
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.

Kudos [?]: [0], given:

Math Expert
Joined: 02 Sep 2009
Posts: 43348

Kudos [?]: 139696 [0], given: 12794

Re: What is the value of a? [#permalink]

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01 Sep 2010, 06:40
HustleHarder wrote:
What is the value of a?

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

[Reveal] Spoiler:
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).
_________________

Kudos [?]: 139696 [0], given: 12794

Non-Human User
Joined: 09 Sep 2013
Posts: 14201

Kudos [?]: 291 [0], given: 0

Re: What is the value of a? [#permalink]

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14 Aug 2017, 05:28
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Kudos [?]: 291 [0], given: 0

Manager
Joined: 06 Jul 2014
Posts: 104

Kudos [?]: 44 [0], given: 179

Location: India
Concentration: Finance, Entrepreneurship
GMAT 1: 640 Q48 V30
Re: What is the value of a? [#permalink]

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14 Aug 2017, 05:46
1st statement is definitely not sufficient.
2nd statement is sufficient if you add a to both sides. 2a=0 => a=0

Kudos [?]: 44 [0], given: 179

Target Test Prep Representative
Status: Founder & CEO
Affiliations: Target Test Prep
Joined: 14 Oct 2015
Posts: 2056

Kudos [?]: 1089 [0], given: 4

Location: United States (CA)
Re: What is the value of a? [#permalink]

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24 Aug 2017, 12:38
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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Scott Woodbury-Stewart
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Kudos [?]: 1089 [0], given: 4

Re: What is the value of a?   [#permalink] 24 Aug 2017, 12:38
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