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Geometry - Lines & Angles

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by Frankenstein » Thu Jun 23, 2011 1:43 am
Hi,
Sum of angles of a triangle is 180 degrees
So, a+c+e = 180
and b+d+f = 180
So, a + b + c + d + e + f = 360

Hence, D
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by dell2 » Thu Jun 23, 2011 1:46 am
OA is something else :) its not D


OA:[spoiler]A=180[/spoiler]
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by Frankenstein » Thu Jun 23, 2011 2:00 am
dell2 wrote:OA is something else :) its not D


OA:[spoiler]A=180[/spoiler]
Can you name the source?
Last edited by Frankenstein on Thu Jun 23, 2011 2:05 am, edited 1 time in total.
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by dell2 » Thu Jun 23, 2011 2:05 am
Got book from my local coaching center. i think 360 is the only correct answer,that's what i got.maybe some error in the book because i couldn't find any possible way to make it 180 LOL.
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by GMATGuruNY » Thu Jun 23, 2011 3:19 am
Perhaps the OA is 180 because the intention was to reproduce Q10 in the Diagnostic Test in the OG12:

Image

In the star figure above, we're asked to find the sum of the angles measurements of the 5 points of the star.
An easy approach is to plug in for the angle measurements.
The key is to plug in values that follow the rules of geometry:

Let's start with the most unusual shape, the pentagon inside the star. For any polygon with n sides, the sum of the interior angles = (n-2)*180. Thus, the sum of the angles inside the pentagon = (5-2)*180 = 540. There are 5 angles inside the pentagon. To make the math easy, let's plug in 540/5 = 108 for each interior angle.

Each of the adjacent angles must be 180-108 = 72 (see the picture), because the sum of angles that form a straight line must be 180.

There are 5 triangles around the outside of the star. The sum of the angles inside each of these triangles must be 180. This forces each point of the star to be 180-72-72 = 36.

Since the star has 5 points, the sum of the angle measurements of all 5 points is 5*36 = 180.
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by amit2k9 » Thu Jun 23, 2011 3:48 am
yupps different answers for different questions here.

a+...+f = 180+180 = 360
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by winniethepooh » Thu Jun 23, 2011 5:29 am
@ dell2: Whats the answer in your coaching notes?
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by dell2 » Thu Jun 23, 2011 9:39 am
Thanks Mitch you are Great Tutor man awesome job :)

winniethepooh : OA in my book is 180. i thought answer might be wrong but GMATGuRuNY Proved me wrong.all questions are in 700-800 range, so i think 360 will be too easy answer for such high level scores :D
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by GMATGuruNY » Thu Jun 23, 2011 9:48 am
dell2 wrote:Thanks Mitch you are Great Tutor man awesome job :)

winniethepooh : OA in my book is 180. i thought answer might be wrong but GMATGuRuNY Proved me wrong.all questions are in 700-800 range, so i think 360 will be too easy answer for such high level scores :D
Thanks, dell2. Just to be clear: the figure shown in your post is different from that shown in mine and in the OG12. Given your figure (in which the center of the star is a hexagon), the sum of the degree measurements of all the points of the star is 360. Given the figure in the OG12 (in which the center of the star is a pentagon), the sum of the degree measurements of all the points of the star is 180. The question in the OG12 is trickier.
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by dell2 » Thu Jun 23, 2011 9:51 am
Thanks Man. Really Appreciated. Thank You Very Much. :)
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