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GMAT Prep : Geometry Traingles

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by Skywalker » Wed Oct 06, 2010 11:58 am
Hi,

I tried solving the sum by applying several triangle properties but could not get the [spoiler]OA = D[/spoiler]. Can someone pls mention the steps...


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by shovan85 » Wed Oct 06, 2010 12:27 pm
Skywalker wrote:Hi,

I tried solving the sum by applying several triangle properties but could not get the [spoiler]OA = D[/spoiler]. Can someone pls mention the steps...


Image

Thanks
https://www.beatthegmat.com/geometry-t67297.html#302732
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by krishnasrivatsa.n » Wed Oct 06, 2010 10:45 pm
I too tried this question, i think the correct answer will be C, by combining the A & B and using the property "exterior angle will be equal to sum of the two non-adjacent interior angles of a triangle"
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by GMATGuruNY » Thu Oct 07, 2010 5:37 am
When you want to see how the angles in a figure affect each other, plug in twice. Plugging in for the angle measurements makes it much easier to see what's going on. Just be sure to follow the rules of geometry as you plug in:

Angles inside a triangle must add up to 180.
Angles opposite equal sides of a triangle must be equal.
Angles that form a straight line must add up to 180.
etc.

The attached .pdf shows two sets of angle measurements that satisfy the requirements of the figure. In each case, we can see that COD:BAO = 3:1 and that BCO:BAO = 2:1.
Now it's easy to see what we need to answer the question: to determine the value of BAO, we need to know either COD or BCO.

Statement 1:
Tells us COD = 60. Sufficient. (If COD = 60, then plugging into COD:BAO = 3:1 we get 60:BAO = 3:1, and BAO = 20.)

Statement 2:
Tells us BCO = 40. Sufficient. (If BCO = 40, then plugging into BCO:BAO = 2:1 we get 40:BAO = 2:1, and BAO = 20.)

The correct answer is D.
Attachments
Angle_relationships_GMATPrep.pdf
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Last edited by GMATGuruNY on Thu Oct 07, 2010 6:48 am, edited 1 time in total.
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by deepak123gmat » Thu Oct 07, 2010 6:31 am
Hi GMATGuruNY,

COD is 60 but you took 30 and how did you calculated other angles.
Plz explain
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by GMATGuruNY » Thu Oct 07, 2010 6:50 am
deepak123gmat wrote:Hi GMATGuruNY,

COD is 60 but you took 30 and how did you calculated other angles.
Plz explain
In my post above there was a typo, which I just now corrected. Does this allay your confusion?
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