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# DS: triangle/angle (GMATPrep)

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Director
Joined: 14 Sep 2007
Posts: 908
Schools: Kellogg '10

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24 Oct 2007, 07:00
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Can someone explain this to me?
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DS #7.doc [89.5 KiB]

Current Student
Joined: 31 Aug 2007
Posts: 369

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24 Oct 2007, 07:23
I think it's E, you dont know if the triangles are isos or equi.
Director
Joined: 14 Sep 2007
Posts: 908
Schools: Kellogg '10

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24 Oct 2007, 07:24
young_gun wrote:
I think it's E, you dont know if the triangles are isos or equi.

That was my guess (obviously), but alas...
Current Student
Joined: 31 Aug 2007
Posts: 369

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24 Oct 2007, 07:26
actually I change my answer...C, i think x=20
Current Student
Joined: 31 Aug 2007
Posts: 369

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24 Oct 2007, 07:29
I think the key is to realize that you know one of the angles is 90 (right triangle) of the large triangle, and you know the interior angles of the quad is 360...then you just deduce....what is the OA? C, D?
Manager
Joined: 30 Jan 2006
Posts: 62

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24 Oct 2007, 07:35
young_gun wrote:
actually I change my answer...C, i think x=20

The answer is definitely C, but i calculated x to be 45
Director
Joined: 14 Sep 2007
Posts: 908
Schools: Kellogg '10

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24 Oct 2007, 07:53
young_gun wrote:
I think the key is to realize that you know one of the angles is 90 (right triangle) of the large triangle, and you know the interior angles of the quad is 360...then you just deduce....what is the OA? C, D?

The OA is C.

Can you describe how you can deduce it?
Current Student
Joined: 31 Aug 2007
Posts: 369

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24 Oct 2007, 08:03
rca215 wrote:
young_gun wrote:
I think the key is to realize that you know one of the angles is 90 (right triangle) of the large triangle, and you know the interior angles of the quad is 360...then you just deduce....what is the OA? C, D?

The OA is C.

Can you describe how you can deduce it?

big triangle sum of angles=180, one of which we know is 90...so the other 2 equal 90 as well.
sum of quad angles=360, one of which is 90, one of which is x. knowing that the other 2 smaller triangles are the same measure (eqi or iso doesnt matter) we can say that x plus its two adjacent angles is 180. and 180 minus angle Q plus 180 minus angle U plus X, is equal to 270 (270 from 360-90, the sum of the quad angles).
Current Student
Joined: 31 Aug 2007
Posts: 369

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24 Oct 2007, 08:09
1
KUDOS
rca215 wrote:
young_gun wrote:
I think the key is to realize that you know one of the angles is 90 (right triangle) of the large triangle, and you know the interior angles of the quad is 360...then you just deduce....what is the OA? C, D?

The OA is C.

Can you describe how you can deduce it?

here is a crude picture, mate.
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Director
Joined: 14 Sep 2007
Posts: 908
Schools: Kellogg '10

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24 Oct 2007, 08:13
I think I get it now. Thanks a ton for the help!
24 Oct 2007, 08:13
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