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Source: — Data Sufficiency |
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by Night reader » Mon Jan 10, 2011 4:20 pm
GHong14 wrote:Image
Given points r,s,t on the number line, is r+s has midpoint 0

st(1) s is to the right of 0, but we don't know where is r. Not Sufficient
st(2) t-r=t-s OR r=-s; restate question -s + s has midpoint 0, we don't know where is s. Not Sufficient

Combining st(1&2) s is to the right of 0 and -s + s has midpoint 0 => symmetrical assumption. Sufficient

Answer C - Yes 0 is midpoint of r and s
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by prachich1987 » Mon Jan 17, 2011 1:30 pm
GHong14 wrote:Image
Is this question from GMATprep?
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by DarkKnight » Tue Jan 18, 2011 5:02 am
Guys,

I can't understand why Statement A is necessary? Is it possible to have t-r=t-(-s) without having r and s being on the opposite side of zero? Experts please help.

Thanks.
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by Geva@EconomistGMAT » Tue Jan 18, 2011 5:38 am
DarkKnight wrote:Guys,

I can't understand why Statement A is necessary? Is it possible to have t-r=t-(-s) without having r and s being on the opposite side of zero? Experts please help.

Thanks.
Try r=-4, s=-2, t=-1, so that -s is equal to 2, and t=-1 is the midpoint between 2 and -4. This condition satisfies stat. (2), but s and r are both to the left of zero.
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by DarkKnight » Tue Jan 18, 2011 8:25 am
Thanks Geva. Guess I didn't try hard enough to find the number combination on the left side of zero. Much appreciated.
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