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# DS-Angles in a Circle

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Manager
Joined: 21 May 2008
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28 Sep 2008, 00:52
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DS Question.
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DS-Angles in a Circle.doc [78.5 KiB]

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Director
Joined: 23 May 2008
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Re: DS-Angles in a Circle [#permalink]

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28 Sep 2008, 02:10
whats the source of this problem?

triangle BOC is a right isoceles inscribed in a semicricle. Angles should be 45, 45, 90, this is sufficient to solve, but in 2) angle BCO=40. Shouldnt have these discrepencies in GMAT probs. So this is not a real GMAT question or I am wrong about something.

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Manager
Joined: 21 May 2008
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Re: DS-Angles in a Circle [#permalink]

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02 Oct 2008, 08:38
This is from GMATPREP.
Attachment:

Slide1.JPG [ 12.23 KiB | Viewed 907 times ]

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Manager
Joined: 27 Aug 2008
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Re: DS-Angles in a Circle [#permalink]

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02 Oct 2008, 09:39
klb15 wrote:
This is from GMATPREP.
Attachment:
Slide1.JPG

IMO D.

OC=AB (Given)
But also OC=OB (radii of circle)
OC=OB=AB

Let <BAO = y. We must find y.
<BAO = y=<BOA (isoceles triangle)
Let <OCB=<OBC=x (isoceles triangle)

1) <COD =60
=> <COA=180-60=120=<COB+y
Also, <COB=180-2x
=> 180-2x+y=120
=> 2x-y=60...Eq.1
<ABO=180-x=180-2y =>x=2y
Put this in Eq.1
3y=60 =>y=20
Hence sufficient.

2) x=40
180-x=180-2y (triangle ABO, <ABO=180-x & <ABO+2y=180)
=> x=2y
=> y=20
Hence Sufficient.

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VP
Joined: 18 May 2008
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Re: DS-Angles in a Circle [#permalink]

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02 Oct 2008, 23:01
D for the reasoning same as that given by Lalit

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Re: DS-Angles in a Circle   [#permalink] 02 Oct 2008, 23:01
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