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What is the value of a + b ?

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What is the value of a + b ?  [#permalink]

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New post 06 Jun 2016, 04:09
00:00
A
B
C
D
E

Difficulty:

  55% (hard)

Question Stats:

67% (01:58) correct 33% (01:40) wrong based on 115 sessions

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Joined: 05 Jun 2016
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GMAT 1: 710 Q50 V37
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Re: What is the value of a + b ?  [#permalink]

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New post 06 Jun 2016, 10:16
St1:- clearly insufficient.
St2:- clearly insufficient.

(a-b)^2= a^2 + b^2 - 2ab,
Can be used to calculate a^2+b^2, but this will also give the value of (a+b)^2.
Hence two values, so answer is 'E'

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

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New post 06 Jun 2016, 22:14
There are 2 variables (a and b) in the original condition. In order to match the number of variables to the number of equations, we need 2 equations. Since the condition 1) and the condition 2) each has 1 equation, there is high chance that C is the correct answer. Using both the condition 1) and the condition 2), from a=b+3, ab=(b+3)b=2, b^2+3b-2=0, we get b={-3+√ [3^2-4*1*(-1)]}/2, b={-3-√ [3^2-4*1*(-1)]}/2. Hence, since we get 2 answers, the answers are not unique and the conditions are not sufficient. Hence, the correct answer is E.
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Re: What is the value of a + b ?  [#permalink]

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New post 06 Jun 2016, 23:04
Bunuel wrote:
What is the value of a + b ?

(1) a - b = 3

(2) a * b = 2


Statement 1

say a = 6, b = 3, then a-b = 3; a+b= 9
a= 12, b= 9, then a-b = 3, a+b= 21.

Not sufficient.


Statement 2

say a = 2, b = 1, then ab= 2, a+b= 3
a= 4, b= 0.5, then ab = 2; a+b= 4.5

Not sufficient.

[b]Combining Statement 1 and 2/b]

(1) a - b = 3
(2) a * b = 2

\((a+b)^2\) = \((a-b)^2\)+ 4ab

We can get the value of \((a+b)^2\) but not exact value of (a+b). [ There will be 2 value of (a+b)

So Not Sufficient.

Answer is E
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Re: What is the value of a + b ?  [#permalink]

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New post 21 Mar 2018, 00:11
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Re: What is the value of a + b ? &nbs [#permalink] 21 Mar 2018, 00:11
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