GMATPrep Geometry Bugger

unless it specifically says "figure not drawn to scale" you can use the diagram for reference

Hey can you tell me how you arrived on the answer D?

What is the explanation to the OA?

tutonaranjo wrote:unless it specifically says "figure not drawn to scale" you can use the diagram for reference

Problem solving diagrams ARE drawn to scale unless they specifically state otherwise.

On the other hand, data sufficiency diagrams are NOT necessarily drawn to scale. It is NOT safe to rely on the way things look, we can only rely on explicitly stated information.

However, there are a few exceptions to this general rule, one of which is that if a line looks like it's straight, we can rely on it being straight.

Here's the scoop taken directly from the test directions (emphasis mine):

Figures

A figure accompanying a data sufficiency question will conform to the information given in the question but will not necessarily conform to the additional information given in statements (1) and (2).

Lines shown as straight can be assumed to be straight and lines that appear jagged can also be assumed to be straight.

You may assume that the positions of points, angles, regions, etc. exist in the order shown and that angle measures are greater than zero.

All figures lie in a plane unless otherwise indicated.

Name angles like this>
angle BAO = x
angle BOA = x (triangle is isoceles because BO is a radius and it is = CO = AB)
angle OBC = y
angle BCO = y (triangle is isoceles, two sides are radii)
angle BOC = 180 - 2y

Solve this.
angle CAO+ACO+AOC = 180 ... translated this means
x + y + x + 180-2y = 180 solves to>
2x=y
so actually, angles OBC and BCO are 2x

Now...
name angle BDC = z (this was previously named 180-2y)

statement 1 says angle COD = 60
60+z+x = 180 (the are all supplementary right?) another equation>
4x+z = 180 (from triangle BOC angles add 180)

x+z = 120 (equation 1)
-4x-z = -180 (equation 2 multiplied by -1)
-3x=-60
x=20
SUFFICIENT

Statement 2 gives you the value of 2x, so you can figure X

tutonaranjo and Stuart,

Thanks for the insight, will be using that approach from now on