Question

If three angles of a quadrilateral are ${100}^{\circ }$ ,${90}^{\circ }$ and ${85}^{\circ }$, then the fourth angle is _____.

• A. ${100}^{\circ }$
• B. ${85}^{\circ }$
• C. ${65}^{\circ }$
• D. ${75}^{\circ }$

Answer 1

The correct option is B

${85}^{\circ }$

Let the fourth angle be 'x'
The sum of the angles of a quadrilateral is ${360}^{\circ }.$
${100}^{\circ }+{90}^{\circ }+{85}^{\circ }+x^{\circ }={360}^{\circ }$
$x={360}^{\circ }-275$
$x={85}^{\circ }$