Choose values. Let the diameter of the larger circle = 10. In this case, the circumference of the larger circle is 10π. Let the diameter of the medium-sized circle be 6 and the diameter of the smaller circle be 4. In this case, the circumference of the smaller circle is 6π, and the circumference of the smaller circle is 4π. 6π + 4π = 10π. The two quantities are equal.