Question

The diameter of circle A is 9 times as great as the diameter of circle B. The area of circle A is how many times as great as the area of circle B? A) 9 B) 16 C) 81 D) 20 E) 1,543

Answer 1

C) 81

Explanation:

Area of a circle is proportional to the square of the diameter. If the diameter is larger by a factor of 9, the area is larger by a factor of 9² = 81.