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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 05 Jun 2016, 14:02
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54% (01:22) correct 46% (01:22) wrong based on 127 sessions

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What is the value of a – b?

(1) a^2 - b^2 = 9

(2) a^2 - 2ab + b^2 = 1

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

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New post 05 Jun 2016, 14:07
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AbdurRakib wrote:
What is the value of a – b?

(1) a^2 - b^2 = 9

(2) a^2 - 2ab + b^2 = 1


(1) a^2 - b^2 = 9
(a+b) (a-b)= 9

Four possibilities= 1*9, 9*1, -1*-9, -9*-1

Not sufficient.

(2) a^2 - 2ab + b^2 = 1

(a-b)^2= 1

two possibilities for (a-b)= +1, -1

Combining both statements (a-b) can be +1 or -1. Not sufficient

E is the answer
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Re: What is the value of a – b?  [#permalink]

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New post 05 Jun 2016, 14:09
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Re: What is the value of a – b?  [#permalink]

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New post 05 Jun 2016, 14:10
Divyadisha wrote:
AbdurRakib wrote:
What is the value of a – b?

(1) a^2 - b^2 = 9

(2) a^2 - 2ab + b^2 = 1


(1) a^2 - b^2 = 9
(a+b) (a-b)= 9

Four possibilities= 1*9, 9*1, -1*-9, -9*-1
Not sufficient.

(2) a^2 - 2ab + b^2 = 1

(a-b)^2= 1

two possibilities for (a-b)= +1, -1

Combining both statements (a-b) can be +1 or -1. Not sufficient

E is the answer


The highlighted part is not correct. We are not told that a and b are integers, thus a^2 - b^2 = 9 has infinitely many solutions for a and b.
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Re: What is the value of a – b?  [#permalink]

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New post 12 Dec 2018, 06:36
Can anyone help me with 1st option? generally in algebra this is how we write a2-b2=9 mean (a-b)*(a+b)=3*3
a-b=3 & a+b=3

Can anyone help me where I am going wrong?
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Re: What is the value of a – b?   [#permalink] 12 Dec 2018, 06:36
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