AB is a diameter of the circle with centre O, CD is chord of the circle, If ∠BOC = 120°, then the value of ∠ADC is ?

Answer: Option B

From figure ∠BOC = 120
∴ ∠AOC = 180 - 120 = 60
So, ∠ADC = $$\frac{1}{2}$$∠AOC
(Angle made on circumference is half of the angle made on centre)
= $$\frac{1}{2}$$ × 60
So, ∠ADC = 30°