Yesterday, Integrated Learning posted a 700 level GMAT question on our blog. Today, they have followed up with the answer:
Answer: D
Explanation: We recommend redrawing this problem to make it match the description. If we’re going to add a new line ED that will be tangent to the circle at point D, such that line EO will pass through C, it is going to look like the figure below.
Remember that a tangent line will always be perpendicular to a radius, which means that angle ODE is 90º. Triangle OCD is equilateral, since angle x is 60º and two of its sides are equal radii, angles C and D must also be 60º. From that we can say that radius OD is 10, and triangle ODE must be a 30-60-90 triangle.
If the side opposite the 30º angle (angle E) is 10, then the hypotenuse must be twice that, or 20.
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