Shortcut Trick
The sum of all exterior angles of any regular polygon is always 360°.
Sum of interior angles = 360° + 50% of 360° = 360° + 180° = 540°.
The polygon with a sum of interior angles equal to 540° is a regular pentagon (5 sides).
Each interior angle (x) of a regular pentagon = 540° ÷ 5 = 108°.
∴ The correct answer is 108°.
Alternate Method
Given:
Sum of interior angles = Sum of exterior angles + 50% of Sum of exterior angles
Each interior angle = x°
Formula Used:
Sum of interior angles of an n-sided polygon = (n − 2) × 180°
Sum of exterior angles of any polygon = 360°
Each interior angle of a regular polygon = [(n − 2) × 180°] ÷ n
Let the number of sides of the regular polygon be n.
The sum of the exterior angles of any polygon is always 360°.
According to the question, the sum of the interior angles is 50% more than the sum of its exterior angles:
⇒ Sum of interior angles = 360° + 50% of 360°
⇒ Sum of interior angles = 360° + 180° = 540°
We know that the sum of the interior angles of an n-sided polygon is given by the formula:
⇒ (n − 2) × 180° = 540°
⇒ n − 2 = 540° ÷ 180°
⇒ n − 2 = 3
⇒ n = 5
Thus, the polygon is a regular pentagon (n = 5).
Each interior angle of a regular polygon is given by:
⇒ x = [(n − 2) × 180°] ÷ n
⇒ x = (3 × 180°) ÷ 5
⇒ x = 540° ÷ 5
⇒ x = 108°
Why other options are incorrect:
⇒ Option (2) 96°: If each interior angle is 96°, then the number of sides n = 360° ÷ (180° − 96°) = 360° ÷ 84° = 4.28, which is not an integer.
⇒ Option (3) 112°: If each interior angle is 112°, then the number of sides n = 360° ÷ (180° − 112°) = 360° ÷ 68° = 5.29, which is not an integer.
⇒ Option (4) 88°: If each interior angle is 88°, then the number of sides n = 360° ÷ (180° − 88°) = 360° ÷ 92° = 3.91, which is not an integer.
∴ The correct answer is 108°.
Additional Information
Sum of Interior Angles
The sum of the interior angles of any convex polygon with n sides is always (n − 2) × 180°.
Sum of Exterior Angles
The sum of the exterior angles of any convex polygon is always 360°, regardless of the number of sides.
Interior and Exterior Angle Relationship
At any vertex of a polygon, the interior angle and the exterior angle are supplementary, meaning their sum is always 180°.