1. What is the connection between the diameter and the radius of a circle?

The diameter is TWICE the length of the radius. i.e. d = 2r


The radius is HALF the length of the diameter i.e. r = d / 2

2. How is the diameter of a circle related to the circumference?

The diameter divides into the circumference just over three times ( pi times)

3. What units are used to measure the length of the circumference?

The units used for the circumference will be the same as those given for the radius or the diameter. (Unless you change them!)