DS 1

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DS 1

by GHong14 » Tue Dec 14, 2010 4:03 pm
Can anyone explain why the selected answer is wrong
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by Rahul@gurome » Tue Dec 14, 2010 6:31 pm
Statement 1 is just giving the coordinates of C, so we cannot find the coordinates of the midpoint.
So, (1) is NOT SUFFICIENT.

Statement 2 is just giving the coordinates of D, so we cannot find the coordinates of the midpoint.
So, (2) is NOT SUFFICIENT.

Combining statements (1) and (2), we can definitely answer the question as we know the coordinates of C and D, both. So applying the midpoint formula, the question can be answered.

[spoiler]The correct answer is C.[/spoiler]
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by ov25 » Tue Dec 14, 2010 6:54 pm
I would leave this to the experts! I think it's E

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by ov25 » Tue Dec 14, 2010 6:57 pm
Gurome I could not resolve the a and b to calculate the mid point. Can you help me here?

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by Rahul@gurome » Tue Dec 14, 2010 6:58 pm
ov25 wrote:I would leave this to the experts! I think it's E
When we find the coordinates of the midpoint, it is [{a + (1 - a)}/ 2, {(1 - b) + b}/2] = (1/2, 1/2)

So, we are able to find the coordinates. Hence, C is the right answer.
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by Rahul@gurome » Tue Dec 14, 2010 6:59 pm
ov25 wrote:Gurome I could not resolve the a and b to calculate the mid point. Can you help me here?
I hope my explanation helps?
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by nespinoz » Sat Dec 25, 2010 3:39 pm
My GMATs friends the midpoint formula is the following:

(X1,X2) = ((X1+X2)/2 , (Y1+Y2)/2)

Using statement 1 and 2.

The midpoint of CD is:

((A+1-A)/2 , (1-B+B)/2) = (1/2, 1/2)

The answer is C!!!