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GMAT PREP DSQ2

by italian7745 » Mon Nov 16, 2009 3:32 am
At a certain store . each notepad costs x dollars and each marker costs y dollars.If 10$ is enough to buy 5 notepads and 3 markers.Is 10$ enough to buy 4 notepads and 4 markers ??

1) each notepad costs less than 1$
2) 10$ is enough for 11 notepads
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Source: — Data Sufficiency |
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by ershovici » Mon Nov 16, 2009 6:58 am
IMO answer is E

1- less than 1$ could be 0.02$ or 0.99$, and no information about markers (thay may cost 1$ or 3$) not sufficient
2- the same
So E is the best choice
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by palvarez » Mon Nov 16, 2009 8:31 am
5x+3y = 10, is 4x+4y = 10?

2. 11x = 10. Sufficient
1. x < 1 , y > 5/3 and x <> y. 4x+4y = 10 when x = y. when x <> y, 4x+4y <> 10. sufficient. (treat this as a weighted average problem)


D is the answer.
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by ershovici » Mon Nov 16, 2009 9:17 am
From the statement 2 we know that 10$ is enough for 11 notepads, but it doesnt mean that 11 notepads cost 10$ (they can cost 9 dollars and 10 will still be enough)
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by Stuart@KaplanGMAT » Mon Nov 16, 2009 12:21 pm
palvarez wrote:5x+3y = 10, is 4x+4y = 10?

2. 11x = 10. Sufficient
1. x < 1 , y > 5/3 and x <> y. 4x+4y = 10 when x = y. when x <> y, 4x+4y <> 10. sufficient. (treat this as a weighted average problem)


D is the answer.
You've mistranslated the original stem.

"10$ is enough to buy 5 notepads and 3 markers" does not mean that "$10 is the exact cost of 5 notepads and 3 markers".

The original translates as:

5x + 3x <= 10

and our question:

is 4x + 4y <= 10?

Since we have an inequality, not an equation, we can't simply invoke the "# of unknowns vs # of equations" rule that you used to prove sufficiency.
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by palvarez » Mon Nov 16, 2009 1:06 pm
Thanks.
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by italian7745 » Mon Nov 16, 2009 11:49 pm
OA is E
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