Two plane mirrors are inclined at an angle of 20° to each other. Determine the number of images formed when an object is placed between them.

The number of images formed by two mirrors inclined at an angle $θ$ is $\frac{360}{θ}-1$. When the mirrors are inclined at $20°$ to each other, $\frac{360}{20} - 1 = 17$ images will be formed.