Final answer:
The measure of an exterior angle of a regular 20-gon is 18°.
Step-by-step explanation:
To find the measure of an exterior angle of a regular 20-gon, we can use the formula: Exterior angle = 360° / Number of sides. In this case, the number of sides is 20, so the measure of each exterior angle is 360° / 20 = 18°.