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Data Sufficiency Question

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by sparkles3144 » Sun Feb 24, 2013 7:11 pm
I need help with this. Can somebody please explain?

What is the value of x, if x^2 - y^2 = 0

(1) X>= 5
(2) y = -3

I thought the answer is C. When I looked the answer, it was E.

I did this:

(1) Alone is insufficient because it provides no information about Y
(2) Alone is insufficient because it provides no information about X

Together X greater than or equal to 5
So, let's take x = 5
y = - 3

(x+y)(x-y)> 0 ?
(5 - 3) (5 + 3) > 0 ?
Yes.

Therefore, C is the answer.
However, answer is E.

Can somebody tell me where I went wrong?

Thanks!
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Source: — Data Sufficiency |

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by brianlange77 » Sun Feb 24, 2013 7:17 pm
sparkles3144 wrote:I need help with this. Can somebody please explain?

What is the value of x, if x^2 - y^2 = 0

(1) X>= 5
(2) y = -3

I thought the answer is C. When I looked the answer, it was E.

I did this:

(1) Alone is insufficient because it provides no information about Y
(2) Alone is insufficient because it provides no information about X

Together X greater than or equal to 5
So, let's take x = 5
y = - 3

(x+y)(x-y)> 0 ?
(5 - 3) (5 + 3) > 0 ?
Yes.

Therefore, C is the answer.
However, answer is E.

Can somebody tell me where I went wrong?

Thanks!
Can you repost the original question? Is the question looking for 'x' or for whether or not it's greater than zero? Your notes make that unclear.
Thanks.
Brian
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by Brent@GMATPrepNow » Sun Feb 24, 2013 7:18 pm
sparkles3144 wrote:I need help with this. Can somebody please explain?

What is the value of x, if x^2 - y^2 = 0

(1) X>= 5
(2) y = -3

I thought the answer is C. When I looked the answer, it was E.

I did this:

(1) Alone is insufficient because it provides no information about Y
(2) Alone is insufficient because it provides no information about X

Together X greater than or equal to 5
So, let's take x = 5
y = - 3

(x+y)(x-y)> 0 ?
(5 - 3) (5 + 3) > 0 ?
Yes.

Therefore, C is the answer.
However, answer is E.

Can somebody tell me where I went wrong?

Thanks!
Are you sure you transcribed the question correctly?

If x > 5 and y = -3, then it's impossible for x^2 - y^2 to equal 0

Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
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by sparkles3144 » Sun Feb 24, 2013 7:27 pm
Hello,

I am sorry. I made a typo.

It is

What is the value of x, if x^2 - y^2 > 0 ?

(1) x>=5
(2) y = -3

Thanks!
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Posts: 16207
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by Brent@GMATPrepNow » Sun Feb 24, 2013 7:35 pm
sparkles3144 wrote: What is the value of x, if x^2 - y^2 > 0 ?

(1) x>=5
(2) y = -3

Thanks!
Target question: What is the value of x?

Given: x^2 - y^2 > 0

Statement 1: x > 5
x can have several values.
Since we cannot answer the target question with certainty, statement 1 is NOT SUFFICIENT

Statement 2: y = -3
x can have several values.
Since we cannot answer the target question with certainty, statement 2 is NOT SUFFICIENT

Statements 1 and 2 combined:
There are several pair of values that satisfy both conditions. Here are two:
Case a: x = 5 and y = -3
Case b: x = 6 and y = -3
Since we still cannot answer the target question with certainty, the combined statements are NOT SUFFICIENT

Answer = E

Cheers,
Brent Hanneson - Creator of GMATPrepNow.com
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