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# GMATPREP Triangle DS

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Senior Manager
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GMATPREP Triangle DS [#permalink]  20 Sep 2006, 17:58
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Difficulty:

(N/A)

Question Stats:

0% (00:00) correct 0% (00:00) wrong based on 0 sessions
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Prob1.doc [74.5 KiB]

Senior Manager
Joined: 11 Jul 2006
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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.
Intern
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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
Intern
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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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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
SVP
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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

Director
Joined: 09 Aug 2006
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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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