Measuring Angles with a Protractor

1. What is the name of the line on a protractor that goes from 0° to 180°? What is its purpose when measuring angles?

2. Imagine you are measuring an angle and you've lined up one side of the angle with the baseline of the protractor. The other side of the angle lines up halfway between the 50° mark and the 60° mark. What is the measurement of the angle?

3. Explain the difference between using the inner and outer numbers on a protractor when measuring an angle. When would you use the inner numbers, and when would you use the outer numbers?