If a transversal intersects two parallel lines, and the difference of two interior angles on the same side of a transversal is 20°, find the angles.
100°, 80°
Interior angles on same side of transversal are supplementary. Let them be x and y, with x − y = 20. Also x + y = 180. Solving: 2x = 200 ⇒ x = 100, y = 80.