A ring of uniform wire has a total resistance of $24\ \Omega$. A straight wire of resistance $12\ \Omega$ joins two points A and B of the ring, and the radii OA and OB make an angle of $120^\circ$, as the figure shows. A battery is connected between A and B. What is the equivalent resistance between A and B?

Fig. 1: A circle with centre O, drawn as a ring of uniform wire of total resistance 24 ohm. Two points A and B lie on the ring, with radii OA and OB drawn and the angle between them marked 120 degrees. A straight wire of resistance 12 ohm joins A to B as a chord. Two leads, one at A and one at B, go to the sides for a battery.