This activity requires the use of a protractor to measure angles. Students are given a diagram of parallel lines cut by a transversal, as well as a diagram of a triangle with an exterior angle. Students will use the protractor to first determine the measure of each angle in the diagrams and label appropriately (this is on 2nd page). The first page of the activity leads students to investigate the relationships between the various angles. You may choose to change the order of the pages. I use this activity as an introduction to angle relationships and have students work with partners. The key uses the measures found when printed out, but depending on the printer used and thickness of lines, there may be a little difference - I suggest measuring it yourself before handing out to students.