Question

Robin uses a protractor that has no markings on it. If an internal angle of $\angle AOB$ needs to be measured using the same protractor, the measure of $\angle AOB$ is _____.

• A. $30°$
• B. $150°$
• C. $40°$
• D. $150°$

Answer 1

The correct option is C $40°$

Observe that the protractor is divided into $18$ broad equal divisions. Hence, each division on the protractor scale corresponds to $\frac{180}{18}=10°$.
The number of broad divisions between $\angle AOB$ is $4$.
The angle measure of $\angle AOB=$ Number of divisions $\times$ Measure of unit division $=4\times 10°$$=40°$