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GMATPrep - DS Geometry

This topic has 1 member reply
allenkt Senior | Next Rank: 100 Posts Default Avatar
Joined
14 Apr 2007
Posted:
36 messages

GMATPrep - DS Geometry

Post Wed May 09, 2007 9:03 am
Elapsed Time: 00:00
  • Lap #[LAPCOUNT] ([LAPTIME])
    I'm sure there is some property of congruent angles that I don't remember that would help me solve this one but I'll be darned if I know what it is.
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    jayhawk2001 Community Manager
    Joined
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    Post Wed May 09, 2007 3:43 pm
    Nice question !

    OB=OC = radius. So angles BCO and CBO are equal.

    Since AB=OC, we have AB=OC=OB. So angles BAO and BOA are equal.

    Also, exterior angle CBO = sum of interior angles = BOA + BAO

    Let x = BAO. We have

    BAO = x = BOA and CBO = BCO = 2x

    1 - sufficient. COD = 60 implies COA = 120 = COB + BOA
    COB = 180 - 4x (property of triangles)
    COB + BOA = 180 - 4x + x = 180 - 3x = 120.
    We can solve for x and hence get BAO

    2 - sufficient. BCO = 2x. So, we can get x and hence angle BAO.

    Hence D.

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