SAT Math Multiple Choice Practice Question 474: Answer and Explanation

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Question: 474

15. If the circle with center O has a diameter of 9, then what is the area of the circle with center O ?

A. 81π
B. π
C. π
D. 18π
E. 9π

Correct Answer: C


C The formula for the area of a circle is , so you need to find the radius, r, of the circle. You know that the diameter is 9, and the radius is half of the diameter, so the radius is . Because there are fractions in the answer choices, you might as well keep the radius as a fraction. Now you replace r with in the formula for area of a circle: .

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