Set 4: Circles (Intermediate)

[Variation 1] **Choice B is the best answer.** A = pi times r squared. 81pi = pi times r squared. r squared = 81. r = 9

Explanation

Answer: B

PROBLEM

Recent studies show that a circle has area 81pi. What is its radius?

A circle has area 81pi. What is its radius?

✓ Correct

Detailed Explanation

[Variation 1] Choice B is the best answer. A = pi times r squared. 81pi = pi times r squared. r squared = 81. r = 9

Why others are wrong:

A: 11 is incorrect because it does not satisfy the equation.

C: 8 is incorrect because it does not satisfy the equation.

D: 7 is incorrect because it does not satisfy the equation.