The diameter of circle A is half of the radius of circle B. If the diameter of circle B is 40 feet, How long is the radius of a circle A?
The diameter of circle A is half of the radius of circle B, so the radius of circle A is 1/2 of the radius of circle B.
Since the diameter of circle B is 40 feet, the radius of circle B is half of the diameter, which is 40/2 = 20 feet.
Therefore, the radius of circle A is 1/2 of the radius of circle B, which is 1/2 * 20 = 10 feet.