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# GMATPREP Triangle DS

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Senior Manager
Joined: 05 Jun 2005
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20 Sep 2006, 18:58
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Senior Manager
Joined: 11 Jul 2006
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Location: TX

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20 Sep 2006, 20:39
Going with A here

BDC is isoceles so DB= BC

From A we know AD = 6 , hence BC =6 Suff

From B we just know the value of angle , doesn't tell anything about the lenth of any side . InSuff.

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Intern
Joined: 14 Sep 2006
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20 Sep 2006, 21:02
ivymba wrote:

How do we know ADB is isoceles? it doesn't explicitly say that

For 2nd statement, x=36, solving for angle DBC gives us 36
but since we don't know angle ADB, that is insufficient too

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Intern
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20 Sep 2006, 21:42

Angle_ABD = 180 - x - (180-2x) = x = Angle_DAB

So AD = DB = BC, AD is given so we know BC. So S1 is sufficient.

I also agree answer is A I don't see how to get the answer from S2.

carlos

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Manager
Joined: 14 Sep 2006
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Schools: Olin Business School - Washington University

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20 Sep 2006, 23:17
I asked this the other day and got some satisfactory responsesâ€¦you can check out the link here:

http://www.gmatclub.com/phpbb/viewtopic.php?t=35285

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SVP
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20 Sep 2006, 23:35
angle bdc = angle dab +dba = 2x ( exterior angle )

thus dba is x , triangle abd is isosceles and thus bd = 6

bd = bc ( issoceles triangle ) thus bc = 6

st two : gives measure of x and nothing about lenghtes of line segments...insuff

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Director
Joined: 09 Aug 2006
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21 Sep 2006, 10:26
HI All,
Sorry for being late. The answer is definately A. If anyone has doubt as why AD and BD are congruent, here is the rule.

" Exterior angle of a triangle is equal to sum of its remote interior angle"

Here, Exterior angle : BDC = 2x
Remote interior angle : BAD and ABD.

ABD = BDC - BAD = 2x -x = x which is equal to BAD.
Hence ABD = DAB.
AD = BD = 6 = BC.

Hope this helps.

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21 Sep 2006, 10:26
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