Since m∠JOK is 1/5th of the measure of the full circle (we know this because 72° is 1/5th of 360° and 360° is the measure of the whole circle), we know that the measure of minor arc JK will be 1/5th of the circumference of the circle. C = 2πr and we know that r = 5 so the circumference is 10π. 1/5th of that is 2π.
