Mathematics Written Test Questions and Answers for Class 9 focuses on “Another Condition for a Quadrilateral to be a Parallelogram”.
1. If the ratio of four angles of a quadrilateral is ∠A : ∠B : ∠C : ∠D = 1 : 2 : 3 : 4, what is the value of ∠C?
a) 90°
b) 108°
c) 180°
d) 72°
Answer: b
Clarification: Let ∠A = x, then ∠B = 2x, ∠C = 3x and ∠D = 4x
We know that sum of the four angles of a quadrilateral is 360°.
Therefore, ∠A + ∠B + ∠C + ∠D = 360°
x + 2x + 3x + 4x = 360°
10x = 360°.
x = 36°.
Now, ∠C = 3x = 3(36°) = 108°.