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Source: — Data Sufficiency |
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Re: xy-plane

by Stuart@KaplanGMAT » Mon Jan 28, 2008 1:15 pm
molsen wrote:In the xy-plane, the line k passes through the origin and through the point (a,b), where ab does not equal zero. Is b positive?

(1) The slope of line k is negative
(2) a<b

Answer: C
(1) Negative slope means it goes from top left to bottom right, so all of the points will be in the (-,+) quadrant or the (+,-) quadrant. b could be positive or negative, insufficient.

(2) If a < b, the point could be (4,8) or (-5,-3). b could be positive or negative, insufficient.

(1) & (2) From (1), we know that either a is negative aned be is positive or vice-versa. If we also know that a is less than b, we can eliminate all of the (+,-) options, leaving us in the top left quadrant, in which every point is (-,+). Therefore b is definitely positive and, combined, the statements are sufficient: choose (C).
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by hwiya320 » Mon Dec 08, 2008 6:13 pm
ohhhhhhhhhhhhhh

Thanks Stuart
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by alexdallas » Mon Jul 06, 2009 5:25 am
"(2) If a < b, the point could be (4,8) or (-5,-3). b could be positive or negative, insufficient. "

how can the point be (-5,-3)? thats not in Q2 or Q4 as u stated..can u pls explain? thanks.
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by Stuart@KaplanGMAT » Mon Jul 06, 2009 9:28 am
alexdallas wrote:"(2) If a < b, the point could be (4,8) or (-5,-3). b could be positive or negative, insufficient. "

how can the point be (-5,-3)? thats not in Q2 or Q4 as u stated..can u pls explain? thanks.
The point only has to be in Q2 or Q4 based on statement (1). When we evaluate statement (2) by itself, we no longer have that information, all all 4 quadrants are fair game (because ab does not equal 0, we know that the point isn't on one of the axes).

We need both pieces of information, so (C) is the correct choice.
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by alexdallas » Mon Jul 06, 2009 11:48 am
wish i had ur brain Stuart :)

cheers mate, big thanx for sizzling Dallas
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