What is the sum of the interior angles of a quadrilateral?

• A. 180 degrees
• B. 270 degrees
• C. 360 degrees
• D. 540 degrees

Answer: (C)

For any polygon, the interior angles add up to (n − 2) × 180 degrees, where n is the number of sides. A quadrilateral has 4 sides, so the sum is (4 − 2) × 180 = 360 degrees. You can see this by drawing a diagonal to split the shape into two triangles; each triangle’s interior angles total 180 degrees, so together they make 360 degrees. The other numbers come from polygons with different numbers of sides (three sides give 180, five sides give 540), so they don’t apply to a four-sided figure.