Question

In the given figure, AOB is a straight line. If ∠AOC = 40°, ∠COD = 4x° and ∠BOD = 3x°, then ∠COD = ?
(a) 80°
(b) 100°
(c) 120°
(d) 140°

Answer 1

(a) 80°

We have :
$$\begin{gathered} \angle AOC+\angle COD+\angle BOD=180°\left[\text{Since}\mathit{\text{AOB}}\text{is a straight line}\right] \\ \Rightarrow 40+4x+3x=180 \\ \Rightarrow 7x=140 \\ \Rightarrow x=20 \\ \therefore \angle COD=4\times 20°=80° \end{gathered}$$