First, find the circumference of the outer ring. The formula to be used is
C = 2pir
200 = 2pir
r = 31.83 cm
Since, both rings are concentric, just subtract 25 from the radius of the outside ring to find the radius of the inner ring
radius of inner ring = 31.83 - 25
radius of inner ring = 6.83
Then, we use this radius to the formula to find its circumference:
C = 2pi6.83
C = 42.91 cm
