If the diameter of a circle is 10, what is the radius?

The radius of a circle is defined as half the length of the diameter. When the diameter is given as 10, you can find the radius by dividing the diameter by 2.

So, in this case, if the diameter is 10, the calculation for the radius is 10 divided by 2, which equals 5. This is why the radius of the circle is 5. This fundamental relationship between the diameter and radius is standard in geometry and is crucial for understanding properties of circles.