Points a and b lie on a circle with radius 1, and arc ab has length π 3 . what fraction of the circumference of the circle is the length of arc pab

The circumference of the circle is equal to

C = 2πr, where r is the radius of the circle. 
Substituting r = 1, the circumference is equal to
C = 2π

Since the arc ab is π/3, its fraction of the circumference is equal to

Fraction = π/3 ÷ 2π
Fraction = 1/6