GRE Quantitative Practice, Standard Multiple-Choice
In a certain parallelogram, the size of one interior angle exceeds that of another interior angle by D degrees. Which of the following expressions represents the degree measure of the smaller angle?
- 90 – D
- 180 –
- 120 – D
- 90 –
- 180 – D
Let x equal the degree measure of the smaller angle, and let (x + D) equal the degree measure of the larger angle. The two angles are by definition supplementary, which means that their degree measures total 180:
x + (x + D) = 180
Solving for x yields the expression in choice (D), which is the correct answer.