If the circumference of the circle in the diagram above is 20π units, what is the area of triangle ABC?

A . 40 square units
B . 80 square units
C . 80π square units
D . 160 square units
E . 160π square units

Answer: B

Explanation:

The circumference of a circle is equal to 2πr, where r is the radius of the circle. If the circumference of the circle = 20π units, then the radius of the circle is equal to ten units. The base of triangle ABC is the diameter of the circle, which is twice the radius. The base of the triangle is 20 units and the height of the triangle is eight units. The area of a triangle is equal to 1/2 bth where b is the base of the triangle and h is the height of the triangle. The area of triangle ABC = 1/2 × 80 × 20 = 1/2 × 160 = 80 square units.