Geometry

Question Analysis
This question assesses the ability to calculate missing angles in irregular polygons using the sum of interior angles.

Key Concept Explanation
The sum of interior angles for any n-sided polygon is (n - 2) × 180°.
For a pentagon (n = 5), this sum is always 540°, regardless of regularity.

Step-by-Step Solution
Calculate the sum for a pentagon: (5 − 2) × 180° = 540°
Sum the given angles: 100° + 110° + 120° + 130° = 460°
Find the missing angle: 540° − 460° = 80°

Common Mistakes
Using the wrong angle sum formula
Arithmetic errors in summing angles
Forgetting th...