Question

Which circle is bigger – a circle with a radius of 4 or a circle with a diameter of 8? Explain

Answer 1

they are both the same size because the radius is just half of the diameter.
8/4 = 2

Answer 2

They're both the same size, because the radius is always half the diameter, meaning a radius of 4 is the same as a diameter of 8. You'd do 4 × 2, which equals 8. And the diameter is two of the radius (8 ÷ 2 = 4). 

Hope this helps.