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Re: Is │x│=│y│? (1) x - y = 6 (2) x + y = 0 [#permalink]

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12 Jun 2013, 12:27

1

This post received KUDOS

WholeLottaLove wrote:

My first instinct was to manipulate |x|=|y|

x=y OR x=-y

1.) says that x-y=6 which means we can get values for x and y

x=6+y y=x-6

So, for x=y

6+y=y 6=0 (Invalid)

x=x-6 0=6 (Invalid)

So, for x=-y

6+y=-y y=-3

x=-x+6 x=3

Why wouldn't we use that methodology on this problem?

Are you saying that A is sufficient?

In the case \(x=3\) and \(y=-3\) => \(|x|=|y|\).

But if \(x=90\) and \(y=84\) then x - y = 6 but \(|x|\neq{|y|}\).

The question asks you if x=y OR x=-y, you cannot assume that it's true in your solution to find the values of x,y for which it holds ture.
_________________

It is beyond a doubt that all our knowledge that begins with experience.

Re: Is │x│=│y│? (1) x - y = 6 (2) x + y = 0 [#permalink]

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12 Jun 2013, 12:43

I should have worded that better.

I guess that solving the problem they way I did, I would say A is correct.

I see that for x-y=6 there could be many values for x and y, however, it seems like many similar problems are solved by manipulating statements (i.e. x-y=6) and plugging into x=y or x=-y.

I understand how this problem was solved, but I want to understand WHY it was solved the way it was.

As always, thank you for for help.

Zarrolou wrote:

WholeLottaLove wrote:

My first instinct was to manipulate |x|=|y|

x=y OR x=-y

1.) says that x-y=6 which means we can get values for x and y

x=6+y y=x-6

So, for x=y

6+y=y 6=0 (Invalid)

x=x-6 0=6 (Invalid)

So, for x=-y

6+y=-y y=-3

x=-x+6 x=3

Why wouldn't we use that methodology on this problem?

Are you saying that A is sufficient?

In the case \(x=3\) and \(y=-3\) => \(|x|=|y|\).

But if \(x=90\) and \(y=84\) then x - y = 6 but \(|x|\neq{|y|}\).

The question asks you if x=y OR x=-y, you cannot assume that it's true in your solution to find the values of x,y for which it holds ture.

Re: Is │x│=│y│? (1) x - y = 6 (2) x + y = 0 [#permalink]

Show Tags

12 Jun 2013, 12:48

1

This post received KUDOS

WholeLottaLove wrote:

My first instinct was to manipulate |x|=|y|

x=y OR x=-y

1.) says that x-y=6 which means we can get values for x and y

x=6+y y=x-6

So, for x=y

6+y=y 6=0 (Invalid)

x=x-6 0=6 (Invalid)

So, for x=-y

6+y=-y y=-3

x=-x+6 x=3

Why wouldn't we use that methodology on this problem?

When you assume that x=y and solve the equation [x-y = 6], you WILL get invalid solutions as you got because you have anyways assumed that x=y--> x-y = 0;which contradicts the given fact.

However, when you assume that x=-y-->x+y=0, you have inherently assumed that |x| IS equal to |y| and now you are just solving for the values of x and y. Thus, the equation [x-y=6] would really not make any difference for this method.( x-y) could equal anything and you would still get |x| = |y|.
_________________

Re: Is │x│=│y│? (1) x - y = 6 (2) x + y = 0 [#permalink]

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12 Jun 2013, 12:52

Ahhh! That makes sense! I am assuming |x| = |y| when I am trying to verify if it does or does not. Thanks!

vinaymimani wrote:

WholeLottaLove wrote:

My first instinct was to manipulate |x|=|y|

x=y OR x=-y

1.) says that x-y=6 which means we can get values for x and y

x=6+y y=x-6

So, for x=y

6+y=y 6=0 (Invalid)

x=x-6 0=6 (Invalid)

So, for x=-y

6+y=-y y=-3

x=-x+6 x=3

Why wouldn't we use that methodology on this problem?

When you assume that x=y and solve the equation [x-y = 6], you WILL get invalid solutions as you got because you have anyways assumed that x=y--> x-y = 0;which contradicts the given fact.

However, when you assume that x=-y-->x+y=0, you have inherently assumed that |x| IS equal to |y| and now you are just solving for the values of x and y. Thus, the equation [x-y=6] would really not make any difference for this method.( x-y) could equal anything and you would still get |x| = |y|.

Re: Is │x│=│y│? (1) x - y = 6 (2) x + y = 0 [#permalink]

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01 Mar 2015, 15:44

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Re: Is │x│=│y│? (1) x - y = 6 (2) x + y = 0 [#permalink]

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22 Sep 2016, 00:39

Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

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Re: Is │x│=│y│? (1) x - y = 6 (2) x + y = 0 [#permalink]

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01 Oct 2016, 20:22

Look into the question as - we need to find out if the numeric value of A and B are equal or not. Statement1: Case 1 A=12 B=6 A-B=6 or A=-3 and B=3 A-B=6 NOT SUFFICIENT

Statement2: A+B=0 This condition is only possible when both A and B are of same numeric values however their signs are opposite or A and B are both 0. In both the case Mod A= Mod B

Re: Is │x│=│y│? (1) x - y = 6 (2) x + y = 0 [#permalink]

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24 Feb 2017, 03:55

Prompt analysis x and y are real numbers

Superset The answer to this question will be either yes or no.

Translation In order to find the answer, we need: 1# exact value of x and y. 2# 2 equation in x and y to find their exact value 3# any other specific equation or properties to determine if the condition holds true.

Statement analysis St 1: x-y = 6. We take two values for (x,y) i.e. (4,-2) and (3,-3)for former it doesn't hold true and for latter it holds true. INSUFFICIENT

St 2: x +y = 0 or x = -y. Taking mod on both side we can say that |x| = |y|. Answer

Option B

gmatclubot

Re: Is │x│=│y│? (1) x - y = 6 (2) x + y = 0
[#permalink]
24 Feb 2017, 03:55

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