Question

Two angles of a quadrilateral are ${79}^{\circ }$ and ${121}^{\circ }$. If the other two angles are equal, then the equal angles measure

• A. ${85}^{\circ }$
• B. ${80}^{\circ }$
• C. ${75}^{\circ }$
• D. ${70}^{\circ }$

Answer 1

The correct option is B

${80}^{\circ }$

Let the equal angles measure x each.

$\text{Sum of interior angles of a quadrilateral}={360}^{\circ }$

$\Rightarrow x^{\circ }+x^{\circ }+{79}^{\circ }+{121}^{\circ }={360}^{\circ }$

$\Rightarrow 2x={160}^{\circ }$

$\Rightarrow x={80}^{\circ }$
$\therefore$ Each equal angle measures ${80}^{\circ }.$