What is the area of a semicircle with a diameter of 21.5

Area of a circle = PI x R^2

r = 1/2 diameter

r = 21.5/2

r = 10.75

Area of circle = 3.14 x 10.75^2 = 3.14 x 115.5625 = 362.86625 square units.

A semicircle is half a circle:

Area of semicircle = 362.86625 / 2 = 181.433125 square units (round the answer as needed).