Question

In figure, $a={40}^o$. The value of $b$ is

• A. ${20}^o$
• B. ${24}^o$
• C. ${36}^o$
• D. ${120}^o$

Answer 1

The correct option is A ${20}^o$

We can clearly see that, $5b$ and $2a$ are linear angles

And $a={40}^0$

$\Rightarrow 5b+2a={180}^o$

$\Rightarrow 5b+2\times {40}^o={180}^o$

$\Rightarrow 5b+{80}^o={180}^o$

$\Rightarrow 5b={100}^o$

$\Rightarrow b=\frac{{100}^o}{5}$

$\Rightarrow b={20}^o$

So, option $A$ is correct