Interior angles of a regular pentagon.

**The reasoning** For any polygon, the sum of interior angles = (n − 2) × 180°, where n is the number of sides. A pentagon has 5 sides, so: Sum = (5 − 2) × 180° = 3 × 180° = 540° Since it's a **regular** pentagon (all angles equal), divide by 5: Each angle = 540° ÷ 5 = **108°** **Why the wrong options tempt you** **120°** — This is the interior angle of a regular *hexagon* (6 sides). Easy mix-up if you're rushing. **144°** — Interior angle of a regular *decagon* (10 sides). Looks "neat" so students guess it. **150°** — Interior angle of a regular *dodecagon* (12 sides). Another polygon trap. The examiners know students confuse polygons, so they deliberately include angles from other common shapes. **Quick takeaway** Remember the formula: **(n − 2) × 180° ÷ n** — pentagon has 5 sides, so (3 × 180°) ÷ 5 = 108°. Don't guess; calculate every time!