Determine the radius of the penny

9.5 mm

Step-by-step explanation:

The black line on the right of the penny represents the diameter: the measure from edge to edge of a circle.

We want to find the radius, the measure from the center to the edge of the circle. The radius is half of the diameter.

r=d/2

We know that the diameter is 19 millimetres. Substitute 19 in for d.

r=19/2

Divide

r=9.5

The radius is 9.5 millimetres