Geometry

Question Analysis:
This ratio problem combines proportion concepts with parallelogram angle properties.

Key Concept Explanation:
Key principles:
Adjacent angles are supplementary
Their measures can be expressed algebraically when given a ratio

Step-by-Step Solution:
Let the angles be 4x and 5x
Set up equation: 4x + 5x = 180°
Solve: 9x = 180° → x = 20°
Larger angle: 5 × 20° = 100°

Common Mistakes:
Setting the ratio sum to 360° instead of 180°
Misidentifying which angle is larger