Question

In figure $ a=40°$. The value of $ b$ is

5b,

• A. $20°$
• B. $24°$
• C. $36°$
• D. $120°$

Answer 1

The correct option is A

$20°$

Explanation for the correct option:

Given, $a=40°$

Then,$2a=2\times 40=80°$

We know that, the angles formed on the starlight line are equal to $180°$

Then,$5b+2a=180°$

$\Rightarrow$$5b+80=180$

$\Rightarrow$ $5b=180-80$

$\Rightarrow$ $5b=100$

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

$\Rightarrow$ $b=20°$

Hence the correct option is option(A)