Browse · MATH Print → jmc prealgebra senior Problem In trapezoid ABCD, sides AB and CD are parallel, ∠A=2∠D, and ∠C=3∠B. Find ∠B. Solution — click to reveal Since AB∥CD, we have ∠B+∠C=180∘. Since ∠C=3∠B, we have ∠B+3∠B=180∘, so 4∠B=180∘, which means ∠B=180∘/4=45∘. Final answer 45^\circ ← Previous problem Next problem →