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# What is the value of a - b ?

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Math Expert
Joined: 02 Sep 2009
Posts: 50623
What is the value of a - b ?  [#permalink]

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15 Jan 2014, 01:50
00:00

Difficulty:

5% (low)

Question Stats:

80% (00:32) correct 20% (00:42) wrong based on 651 sessions

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The Official Guide For GMAT® Quantitative Review, 2ND Edition

What is the value of a - b ?

(1) a = b + 4
(2) (a - b)^2 = 16

Data Sufficiency
Question: 37
Category: Algebra First- and second- degree equations
Page: 155
Difficulty: 550

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

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15 Jan 2014, 01:50
SOLUTION

What is the value of a - b ?

(1) a = b + 4 --> re-arrange: a-b=4. Sufficient.

(2) (a - b)^2 = 16 --> a-b=4 or a-b=-4. Not sufficient.

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Joined: 14 Oct 2013
Posts: 3
Re: What is the value of a - b ?  [#permalink]

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15 Jan 2014, 23:50
Hi Bunuel,

I think that the second statement is (a-b)² rather than (a-b).
Am I right?

Thanks.
Manager
Joined: 04 Oct 2013
Posts: 152
Location: India
GMAT Date: 05-23-2015
GPA: 3.45
Re: What is the value of a - b ?  [#permalink]

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16 Jan 2014, 00:52
The Question 37, Page 155 in Data Sufficiency Sample Questions of Quant Review is as follows:

What is the value of a - b ?

(1) $$a = b + 4$$
(2) $$(a - b)^2 = 16$$

Solution:

Statement (1)

$$a= b+4$$
Or, $$a-b=4$$
As the value of a-b can be uniquely determined, statement (1) is sufficient.

Statement (2)

Solving the equation, $$(a - b)^2 = 16$$,
we have either $$a-b= 4$$ or $$a-b= -4$$.
As the value of $$a-b$$ can not be uniquely determined, statement (2) is not sufficient.

Math Expert
Joined: 02 Sep 2009
Posts: 50623
Re: What is the value of a - b ?  [#permalink]

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18 Jan 2014, 03:59
SOLUTION

What is the value of a - b ?

(1) a = b + 4 --> re-arrange: a-b=4. Sufficient.

(2) (a - b)^2 = 16 --> a-b=4 or a-b=-4. Not sufficient.

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Joined: 06 Jan 2014
Posts: 39
Re: What is the value of a - b ?  [#permalink]

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18 Jan 2014, 13:49
Bunuel wrote:
SOLUTION

What is the value of a - b ?

(1) a = b + 4 --> re-arrange: a-b=4. Sufficient.

(2) (a - b)^2 = 16 --> a-b=4 or a-b=-4. Not sufficient.

how is 1 sufficient when a & b can still be any combination of numbers i.e. (0,4), (1,5) (2,6).....and on and on
Math Expert
Joined: 02 Sep 2009
Posts: 50623
Re: What is the value of a - b ?  [#permalink]

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19 Jan 2014, 09:36
1
TroyfontaineMacon wrote:
Bunuel wrote:
SOLUTION

What is the value of a - b ?

(1) a = b + 4 --> re-arrange: a-b=4. Sufficient.

(2) (a - b)^2 = 16 --> a-b=4 or a-b=-4. Not sufficient.

how is 1 sufficient when a & b can still be any combination of numbers i.e. (0,4), (1,5) (2,6).....and on and on

Yes but we are asked to find the value of a-b, not the individual values of a and b.
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Joined: 21 May 2013
Posts: 652
Re: What is the value of a - b ?  [#permalink]

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27 Nov 2014, 06:23
Bunuel wrote:
TroyfontaineMacon wrote:
Bunuel wrote:
SOLUTION

What is the value of a - b ?

(1) a = b + 4 --> re-arrange: a-b=4. Sufficient.

(2) (a - b)^2 = 16 --> a-b=4 or a-b=-4. Not sufficient.

how is 1 sufficient when a & b can still be any combination of numbers i.e. (0,4), (1,5) (2,6).....and on and on

Yes but we are asked to find the value of a-b, not the individual values of a and b.

Hi Bunuel,

I have learnt from GMATClub that the root of a positive number is always positive-so root of 16 should only be 4 right (for GMAT purposes). So-the answer should be D right?
Math Expert
Joined: 02 Sep 2009
Posts: 50623
Re: What is the value of a - b ?  [#permalink]

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27 Nov 2014, 06:27
KS15 wrote:
Bunuel wrote:
TroyfontaineMacon wrote:

how is 1 sufficient when a & b can still be any combination of numbers i.e. (0,4), (1,5) (2,6).....and on and on

Yes but we are asked to find the value of a-b, not the individual values of a and b.

Hi Bunuel,

I have learnt from GMATClub that the root of a positive number is always positive-so root of 16 should only be 4 right (for GMAT purposes). So-the answer should be D right?

When the GMAT provides the square root sign for an even root, such as a square root, fourth root, etc. then the only accepted answer is the positive root. That is:

$$\sqrt{9} = 3$$, NOT +3 or -3;
$$\sqrt[4]{16} = 2$$, NOT +2 or -2;

Notice that in contrast, the equation $$x^2 = 9$$ has TWO solutions, +3 and -3. Because $$x^2 = 9$$ means that $$x =-\sqrt{9}=-3$$ or $$x=\sqrt{9}=3$$.
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Concentration: Finance, Entrepreneurship
GMAT 1: 650 Q47 V34
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Re: What is the value of a - b ?  [#permalink]

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23 Mar 2017, 10:40
Is this really a 550-level question?
Looks like 400-level one
Just kidding......;
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Re: What is the value of a - b ? &nbs [#permalink] 23 Mar 2017, 10:40
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