Question

$\angle A$ and $\angle B$ form a linear pair. If $m\angle A={80}^o$, what is the measure of $\angle B$?

• A. ${80}^o$
• B. ${100}^o$
• C. ${180}^o$
• D. None of the above

Answer 1

The correct option is B ${100}^o$

$\underset{–}{\text{Given:}}$
$\bullet$$\angle A$ and $\angle B$ form a linear pair.
$\bullet$ $m\angle A={80}^o$

$\underset{–}{\text{Linear Pair:}}$
Pair of adjacent angles whose non-common sides form a straight line and their measures add up to ${180}^o$.

$\because$ $\angle A$ and $\angle B$ form a linear pair.
$\Rightarrow$ $m\angle A+m\angle B={180}^o$
$\Rightarrow$ ${80}^o+m\angle B={180}^o$
Subtracting ${80}^o$ from both sides,
$\Rightarrow$ ${80}^o+m\angle B-{80}^o={180}^o-{80}^o$
$\Rightarrow$ $m\angle B={100}^o$

So, option(b.) is correct.