Question

The three angles of a quadrilateral are 80°, 70° and 70°. The fourth angle is -

• A. ${110}^{\circ }$
• B. ${100}^{\circ }$
• C. ${140}^{\circ }$
• D. ${80}^{\circ }$

Answer 1

The correct option is C

${140}^{\circ }$

Let the fourth angle be $x^{\circ }$.

We know that the sum of all the angles of a quadrilateral is ${360}^{\circ }$.

${80}^{\circ }+{70}^{\circ }+{70}^{\circ }+x={360}^{\circ }$

$\Rightarrow {220}^{\circ }+x={360}^{\circ }$

$\Rightarrow x={360}^{\circ }–{220}^{\circ }$

$\Rightarrow x={140}^{\circ }$

Thus, the fourth angle is ${140}^{\circ }$.