Set 5: Circles (Beginner)

[Variation 1] **Choice D is the best answer.** Circumference = 2 times pi times r = 2 times pi times 9 = 18pi

Explanation

Answer: D

PROBLEM

Recent studies show that a circle has radius 9. What is its circumference? (Express answer as a number times pi)

A circle has radius 9. What is its circumference? (Express answer as a number times pi)

20pi

9pi

81pi

18pi

✓ Correct

Detailed Explanation

[Variation 1] Choice D is the best answer. Circumference = 2 times pi times r = 2 times pi times 9 = 18pi

Why others are wrong:

A: 20pi is incorrect because it does not satisfy the equation.

B: 9pi is incorrect because it does not satisfy the equation.

C: 81pi is incorrect because it does not satisfy the equation.