Refreshing GMAT Quant: Parallel Lines and Angles

Let’s look at this GMath problem to take a little time to review all the relationships that angles and transversal lines can create!









If line AC bisects angle BCD, what is the measure of angle ADC?

(A) 20 degrees
(B) 30 degrees
(C) 40 degrees
(D) 45 degrees
(E) 50 degrees

The lines/angles and triangles rules to refresh for this one:

-When two parallel lines are cut by a transversal, corresponding angles are equal
-Vertical angles are equal
-Supplemental angles sum to 180 degrees
-All the angles around one point sum to 360 degrees
-All three angles in a Triangle sum to 180 degrees

If you know all those rules and are comfortable with “extending lines,” then this question isn’t too challenging. :blushing

Let’s “fill this in”!














The correct answer is (B).