A circle has a circumference of 18 inches. What is the area, in square inches, of the circle?

SAT Circles Practice Question 9 (Easy)

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Math · Geometry and TrigonometryEasy

A circle has a circumference of $18\pi$ inches. What is the area, in square inches, of the circle?

$9\pi$

$36\pi$

$81\pi$

$324\pi$

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Answer: C

From $2\pi r = 18\pi$ , the radius is $r = 9$ inches. The area is $\pi r^2 = \pi(9)^2 = 81\pi$ square inches.

Choice D uses $18$ as the radius, but $18$ is the diameter.

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