In the triangle above, what is the length of the side BC? : GMAT Data Sufficiency (DS)
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In the triangle above, what is the length of the side BC?

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In the triangle above, what is the length of the side BC? [#permalink]

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New post 10 Apr 2010, 03:50
00:00
A
B
C
D
E

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In the triangle above, what is the length of the side BC?

(1) Line segment AD has length 6
(2) x= 36

Can someone please explain the logic behind the explanation given in the official guide for the quantitative review-1st edition (question #117).

What I can't understand from the explanation is that it has been assumed that

angle ABD + angle DAB = 2x

will imply that ABD = DAB =x.

Why is the above true? Isn't it possible that ABD = 1.5x and DAB = 0.5x?

Why those two have to be equal?
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Re: Quantitative Review #117 [#permalink]

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New post 10 Apr 2010, 04:30
LM wrote:
Can someone please explain the logic behind the explanation given in the official guide for the quantitative review-1st edition (question #117).

In the triangle above, what is the length of the side BC?

(1) Line segment AD has length 6

(2) x= 36

What I can't understand from the explanation is that it has been assumed that

angle ABD + angle DAB = 2x

will imply that ABD = DAB =x.

Why is the above true? Isn't it possible that ABD = 1.5x and DAB = 0.5x?

Why those two have to be equal?


We can no way assume that ABD=DAB=x, from ABD+DAB=2x. If we knew that either ABD or DAB equals to x, then the answer would be A. But in it's current form the answer should be E.
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Re: Quantitative Review #117 [#permalink]

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New post 10 Apr 2010, 16:28
Bunuel wrote:
LM wrote:
Can someone please explain the logic behind the explanation given in the official guide for the quantitative review-1st edition (question #117).

In the triangle above, what is the length of the side BC?

(1) Line segment AD has length 6

(2) x= 36

What I can't understand from the explanation is that it has been assumed that

angle ABD + angle DAB = 2x

will imply that ABD = DAB =x.

Why is the above true? Isn't it possible that ABD = 1.5x and DAB = 0.5x?

Why those two have to be equal?


We can no way assume that ABD=DAB=x, from ABD+DAB=2x. If we knew that either ABD or DAB equals to x, then the answer would be A. But in it's current form the answer should be E.



This means that the Official Guide has the wrong answer. Official Guide gives the answer as "A", but I thought ( same as you!) that the answer should be"E".
whom shall we inform if the answer in the Official Guide is wrong?
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Re: Quantitative Review #117 [#permalink]

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New post 10 Apr 2010, 18:09
In my OG Quant 1 DAB=x.
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Re: Quantitative Review #117 [#permalink]

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New post 10 Apr 2010, 20:12
walker wrote:
In my OG Quant 1 DAB=x.


Walker,

I checked it again, and I believe they have not published two versions of Quant-I (review). :shock:

The official guide, page number 193, shows that BDC = 2x and BCD = 2x.

That's why I thought somehow the explanation or rather the answer given in the OG is incorrect. :shock:
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Re: Quantitative Review #117 [#permalink]

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New post 16 Apr 2010, 03:58
I think LM is right
Even in my quant, nothing is mentioned about angle DAB

explanation by OG - let angle DBA be y , so x + y = 2x (exterior angle) so x =y .........(but nowhere they mention that DAB is x)

Can official guide be wrong??? Surprise Surprise
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Re: Quantitative Review #117   [#permalink] 16 Apr 2010, 03:58
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