Students join the Riverton road crew to find the missing corners of ten triangular traffic islands. They use the triangle angle sum (180°) and the exterior angle theorem, while a running total catches slips like 185° before they move on. Correct angles label the island drawing. Auto-graded, randomized, Grade 8, 8.G.A.5.
Triangle Angle Sum and Exterior Angles: Grade 8 Practice Worksheet (8.G.A.5)
Help your Grade 8 students master the triangle angle sum theorem and the exterior angle theorem with a real-world, auto-graded geometry worksheet. Students join the Riverton road crew as it builds triangle-shaped traffic islands where three roads meet. The surveyor measured only some of each island’s corners, and students use angle facts to find the rest so the curb forms can be cut to fit.
What students do
Built-in self-check
A running readout adds up the student’s own angles as they type. If they make an arithmetic slip, they see “That is 185°, not 180°” right away and fix it before moving on. In Part 2, the readout checks that the two remote interior angles really add up to the exterior angle. When an answer is correct, its value appears on the scale drawing of the island, so students see their progress build.
Why teachers use it
Great for
Grade 8 math, pre-algebra and middle school geometry units on triangle angle sum, exterior angles, remote interior angles, supplementary angles and linear pairs, and finding missing angles in triangles.
Students find missing angles in ten triangular traffic islands, first by using the fact that a triangle’s interior angles sum to 180° and then by using the exterior angle theorem. A running self-check total shows any arithmetic slip, and the final island ties both facts together through a linear pair. This builds fluency with the triangle angle-sum and exterior-angle facts (8.G.A.5).
The worksheet support randomization. If you enable it every students will receive different angles to work. This prevent copying of answers.
💡 Tip: When assigning this activity to your classroom, you can optionally enable randomization to give each student a unique version of the problems. When you re-assign the same worksheet, each student will get a new set of questions, helping them master the content through repeated practice.
Use informal arguments to establish facts about the angle sum and exterior angle of triangles, about the angles created when parallel lines are cut by a transversal, and the angle-angle criterion for similarity of triangles. *For example, arrange three copies of the same triangle so that the sum of the three angles appears to form a line, and give an argument in terms of transversals why this is so*.
All 8.G.A.5 activities →More interactive, auto-graded activities on the same standards and topics.
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