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HELP! The book is definitely wrong on this one.

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Source: — Data Sufficiency |
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by Stuart@KaplanGMAT » Fri Jun 18, 2010 2:14 pm
thaipq5290 wrote:Q: If x>0, is x>y

(1) 5x-4y=3
(2) 4y-5x=3

OA is C

But for me: (2) => y=(3+5x)/4 which shows that y > x

x>0 => 5x+3>5x => (5x+3)/4>5x/4>x, y=(5x+3)/4>x => (2) is sufficient => B
Here's another way to show that (2) is sufficient alone:

4y - 5x = 3

4y = 5x + 3

y = (5/4)x + 3/4

Since x is positive, (5/4)x is greater than x. So:

y = (bigger than x) + 3/4

which is definitely bigger than x.
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by blaster » Sat Jun 19, 2010 1:04 am
(2) 4y-5x=3
here we can see without any calculation that y>x . because 4 y minus 5x results positive number.
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