If a circle's diameter is 10, what is the radius?

If a circle's diameter is 10, what is the radius?

• A. 10
• B. 7.5
• C. 5
• D. 2.5

Answer: (C)

The radius is half of the diameter. The diameter is the distance across the circle through the center, while the radius is the distance from the center to the edge. So with a diameter of 10, the radius is 10 ÷ 2 = 5. This keeps the relationship consistent: diameter equals twice the radius. A radius of 10 would imply a diameter of 20, a radius of 7.5 would imply a diameter of 15, and a radius of 2.5 would imply a diameter of 5, none of which match the given diameter of 10.

The radius is half of the diameter. The diameter is the distance across the circle through the center, while the radius is the distance from the center to the edge. So with a diameter of 10, the radius is 10 ÷ 2 = 5. This keeps the relationship consistent: diameter equals twice the radius. A radius of 10 would imply a diameter of 20, a radius of 7.5 would imply a diameter of 15, and a radius of 2.5 would imply a diameter of 5, none of which match the given diameter of 10.