This activity develops an understanding of the degree as a unit of rotation used to measure angles and introduces students to the protractor.

By now students have encountered many angle measurements and have some intuitive awareness of the sizes relative to a full turn (), half of a full turn (), and a quarter of a full turn (). In this activity, students learn that a angle is of a full turn and that an angle that is composed of angles has a measurement of . For example, a  angle is made up of seven angles.

• “How did you find out the size of the two angles when the protractors show no numbers or scales?” (We know that the turn from one tick mark to the next is . We can use the tick marks to count the number of turns. We can imagine the tick marks split the angle into a number of angles. We can count each angle to find the measurement.)

In this activity, students learn how to use a protractor. They align a protractor to the vertex and a ray of an angle so that its measurement can be read. The given angles are oriented in different ways, drawing students’ attention to the two sets of scales on a protractor. Students need to consider which set of numbers to pay attention to and think about a possible explanation for when or how to use each scale. Moreover, one of the scales is only marked in increments of 10 degrees, so if students use this scale, they need to reason carefully about the precise angle measure (MP6).

This activity uses MLR1 Stronger and Clearer Each Time. Advances: reading, writing.

• Select students who used different strategies to share their responses and reasoning.
• Display the image of Elena and Kiran’s angle. If no students mentioned that is not possible because the angle clearly appears greater than a right angle (), consider asking how Elena can use what she knows about right angles to think about her measurement.