If a circle has radius 5, what is its diameter?

If a circle has radius 5, what is its diameter?

• A. 5
• B. 10
• C. 20
• D. 15

Answer: (B)

The diameter of a circle is twice its radius, because it stretches from one side of the circle to the other through the center. So with a radius of 5, the diameter is 2 × 5 = 10. The other numbers are multiples of the radius that don’t represent across-the-circle distance: 5 is the radius itself, 15 is three times the radius, and 20 is four times. Therefore, the diameter is 10.

The diameter of a circle is twice its radius, because it stretches from one side of the circle to the other through the center. So with a radius of 5, the diameter is 2 × 5 = 10. The other numbers are multiples of the radius that don’t represent across-the-circle distance: 5 is the radius itself, 15 is three times the radius, and 20 is four times. Therefore, the diameter is 10.