Question

what part of the circumference is an arc whose measure is 30

Answer 1

Circumference of a circle:
C = 2 r π;
Length of an arc:
L = r π α / 180°
L = r π · 30° / 180° = r π /6
r π /6   :   2 r π = 1/6 : 2 = 1/12

= 1/2