# Question #bd668

If each interior angle is ${170}^{o}$, then the exterior angle adjacent to it is ${10}^{o}$ since the interior angle and its adjacent exterior angle add to ${180}^{o}$.
The sum of the exterior angles of any polygon is ${360}^{o}$. Divide ${360}^{o}$ by the measure of each exterior angle, ${10}^{o}$. The quotient, 36, tells us not only that there are 36 exterior angles, but also that there are 36 sides to the polygon, since the number of exterior angles equals the number of sides.