SAT Question fb58c0db: Circles answer and explanation with Desmos solution

The circumference, $C$, of a circle is $C=2\pi r$, where $r$ is the length of the radius of the circle. For the given circle with a radius of $1$, the circumference is $C=2\pi \times 1$, or $C=2\pi$. To find what fraction of the circumference the length of arc $AB$ is, divide the length of the arc by the circumference, which gives $\frac{\pi }{3}÷2\pi$. This division can be represented by $\frac{\pi }{3}\times \frac{1}{2\pi }=\frac{1}{6}$. Note that 1/6, .1666, .1667, 0.166, and 0.167 are examples of ways to enter a correct answer.