Answer:
To find the button's radius, we need to divide its diameter by 2, since the radius is half the size of the diameter.
radius = diameter ÷ 2
Given that the diameter of Ted's button is 10 millimeters, we can substitute it into the above formula to get:
radius = 10 mm ÷ 2
radius = 5 mm
Therefore, the button's radius is 5 millimeters.