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Geometry and TrigonometryEasy–MediumComparing circumferences

Geometry and Trigonometry practice question

Circle P has a radius of 3 and circle Q has a radius of 6. Which statement is true?

  1. A. Q's circumference is 2 times P's, and Q's area is 4 times P's.Correct
  2. B. Q's circumference is 4 times P's, and Q's area is 2 times P's.
  3. C. Q's circumference and area are both 2 times P's.
  4. D. Q's circumference and area are both 4 times P's.

Answer: A. Q's circumference is 2 times P's, and Q's area is 4 times P's.

Circumference scales with r (×2); area scales with r² (×4).

Why the other answers are wrong

B. Q's circumference is 4 times P's, and Q's area is 2 times P's.
Swapped.
C. Q's circumference and area are both 2 times P's.
Area scales with the square of the radius.
D. Q's circumference and area are both 4 times P's.
Circumference scales with the radius, not its square.

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