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salr15
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GMAT PREP - Geom Question 29 Apr 2007, 16:27
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Hi can you please explain this to me:





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GMAT PREP - Geom Question 29 Apr 2007, 16:41
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What is true about the left triangle?
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salr15
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GMAT PREP - Geom Question 29 Apr 2007, 17:09
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That is what I am trying to figure out. My answer was C but the correct answer is A.

I don't understand how with what is given you can use AD = 6 to find BC.
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GMAT PREP - Geom Question 29 Apr 2007, 20:58
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I got A by using substitution.


Since you know that angle BDC and BCD are the same (2X), you know that triangle DBC is issoc. triangle. So the question can be what is BD since BD = BC


You know the angles of ABC = 180, and angle BAC is X and angle BCA is 2X, angle ABC must be 180 - 3x

To solve for ABD, ABC - DBC:

(180 - 3x) - (180 - 4X) = X

So now you know ABD is also X.

Thus, BD must equal AD (which is 6).

Hope this explains it.

Another hint is: It's too obvious that the answer is C. GMAT likes to pull tricks like this.
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GMAT PREP - Geom Question 30 Apr 2007, 01:59
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St1:
<ADB = 180-2x
<ABD = 180-x-180+2x = x
So AD = BD = 6
Since BD = BC, so BC = 6. Sufficient.

St2:
Insufficient. Can't derive the length in any way.

Ans A



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