Q. 4 A3.9( 50 Votes )

# ABCD is a parallelogram. The ratio of ∠A and ∠B of this parallelogram is 5 : 4. Find the measure of ∠B.

Answer :

Given: ∠A : ∠B = 5:4

Let the measure of ∠A = 5x

Then ∠B = 4x

Since the adjacent angles of a parallelogram are complementary, therefore ∠A + ∠B = 180°

⇒ 5x + 4x = 180°

⇒ 9x = 180°

⇒ x = 20°

∴ ∠ A = 5x = 5 × 20° = 100°

∴ ∠ B = 4x = 4 × 20° = 80°

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