If the diameter of a circle is 12 cm, what is its radius?

Correct answer: 6. Radius = diameter ÷ 2 = 12 ÷ 2 = 6 cm.

Background: The diameter is twice the radius.

• 9: 9 cm is not half of 12 cm.
• 12: 12 cm is the diameter.
• 18: 18 cm is more than the diameter.

Did you know? The circumference is 2πr = 12π cm.

Memory trick: Radius = half of diameter.