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 Post subject: Data Sufficiency Question - From Page 106, Question #82Posted: Tue Aug 03, 2010 5:35 pm

Joined: Tue Aug 03, 2010 4:19 pm
Posts: 1
Can someone help me with this one? Really struggling...

If x+y = 6, what does x-y equal?

(1) X^2 – y^2 = 12

(2) 2y +x = 8

Thanks!

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 Post subject: Re: Data Sufficiency Question - From Page 106, Question #82Posted: Tue Aug 03, 2010 7:19 pm

Joined: Tue Aug 03, 2010 5:05 pm
Posts: 3
Location: Toronto
This is one of those DS problems that tries to trick you into guessing that only one of the statements is sufficient.

First let's focus on what we know, which is x+y=6

Second let's "jump ahead" to statement 2. It is a second distinct equation. Therefore with 2 equations and 2 unknowns we can solve for both x and y. So statement 2 is sufficient.

Now let's go to statement 1. Many people will dismiss this statement as insufficient. However if we break the equation down to
(x+y)(x-y)=12

We know that x+y=6, therefore x-y=2. Sometimes we don't have to know what the individual values for x and y are. We just need to know what x-y is equal to. Statement 1 is sufficient.

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