Three consecutive angles of a cyclic quadrilateral are in

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Three consecutive angles of a cyclic quadrilateral are in the ratio of 1 : 4 : 5. The measure of fourth angle is :

1. 120°
2. 60°
3. 30°
4. 80°

Correct Option: B

Here , Ratio of angles = 1 : 4 : 5
The sum of the opposite angles of a cyclic quadrilateral is 180°.
For a quadrilateral ABCD,
∠A = y°; ∠B = 4y°; ∠C = 5y°
∴ x + 5y = 180° ⇒ 6y = 180°

⇒ y =	180°	= 30°
	6

∴ ∠B + ∠D = 180°
⇒ 4 × 30° + ∠D = 180°
⇒ ∠D = 180° – 120° = 60°