UPCAT Mathematics practice question 45: What is the measure of each interior angle of a regular pentagon?
Correct answer
A. 108°
The interior angles total (5 − 2) × 180° = 540°, and 540° ÷ 5 = 108°. The 72° figure is the exterior angle.
The question
What is the measure of each interior angle of a regular pentagon?
- Option A: 108°Correct
- Option B: 72°
- Option C: 100°
- Option D: 120°
Why A is correct
The interior angles total (5 − 2) × 180° = 540°, and 540° ÷ 5 = 108°. The 72° figure is the exterior angle.
Why the other options are wrong
- B 72°
- This is the *exterior* angle. Interior and exterior are supplementary here, so 180 − 72 = 108.
- C 100°
- A rounding-flavoured guess; 540 ÷ 5 is exactly 108.
- D 120°
- The interior angle of a regular *hexagon*, not a pentagon.