What is the value of y?

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What is the value of y?

by amirhakimi » Sun Dec 15, 2013 9:04 am
What is the value of y?

(1) 3|x2 - 4| = y - 2

(2) |3 - y| = 11

It's From MGMAT CAT and Answer is C
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Amir,

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by Brent@GMATPrepNow » Sun Dec 15, 2013 9:38 am
amirhakimi wrote:What is the value of y?

(1) 3|x² - 4| = y - 2
(2) |3 - y| = 11

Target question: What is the value of y?

Statement 1: 3|x² - 4| = y - 2
Tons of possible values for y. Here are two cases:
Case a: x = 0, in which case y = 14
Case b: x = 1, in which case y = 11
Since we cannot answer the target question with certainty, statement 1 is NOT SUFFICIENT

Statement 2: |3 - y| = 11
If |something| = k (where k > 0), then something = k, or something = -k

So, we get two possible equations:
3 - y = 11, in which case y = -8
3 - y = -11, in which case y = 14
Since we cannot answer the target question with certainty, statement 2 is NOT SUFFICIENT

Statements 1 and 2 combined
Statement 2 tells us that y equals EITHER -8 OR 14
Statement 1 tells us that 3|x² - 4| = y - 2
Since absolute values are always greater than or equal to 0, we know that y - 2 > 0
This means that y >2
If y >2, then we can rule out the possibility that y = -8, which means y MUST equal 14

Since we can answer the target question with certainty, the combined statements are SUFFICIENT

Answer = C

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Brent
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by j_shreyans » Fri Jan 30, 2015 2:46 am
Hi Brent ,

Statement 1: 3|x² - 4| = y - 2

Can we solve the statement 1 by changing the sign like below.

3x^2-12=y-2

3x^2-y=10 .......(|)

and

3x^2-12=-y+2

3x^2+y=14..........(||)


Please suggest and correct me if i am wrong.

Thanks

Shreyans