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Geometry and Trigonometry / Area and volume Difficulty: Medium

A circle has a circumference of $31 pi$ centimeters. What is the diameter, in centimeters, of the circle?

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Explanation

The correct answer is $31$ . The circumference of a circle is equal to $2 pi r$ centimeters, where $r$ represents the radius, in centimeters, of the circle, and the diameter of the circle is equal to $2 r$ centimeters. It's given that a circle has a circumference of $31 pi$ centimeters. Therefore, $31 pi equals 2 pi r$ . Dividing both sides of this equation by $π$ yields $31 equals 2 r$ . Since the diameter of the circle is equal to $2 r$ centimeters, it follows that the diameter, in centimeters, of the circle is $31$ .