Angles of a triangle: the sum and the exterior angle

Answer Key - Grade 8 Math Worksheet - Building Confidence

Circle the best answer, or write your answer on the line.

1. 1.

   Bo measures a paper triangle. Two of its angles are 53° and 39°. The sketch writes 180° beside the triangle. What is the third angle?

   88
2. 2.

   Jun measures a triangular kite wing. Two of its angles are 62° and 64°. The sketch writes 180° beside the triangle. What is the third angle?

   54
3. 3.

   Luz draws triangle GHQ and extends side GH past corner H. The inside angle at H is 38°. The sketch writes 180° along the straight line. How many degrees is the outside angle at H?

   142
4. 4.

   Milo draws triangle SUV and extends side SU past corner U. The inside angle at U is 71°. The sketch writes 180° along the straight line. How many degrees is the outside angle at U?

   109
5. 5.

   Noah draws triangle WYC and extends side WY past corner Y. The inside angle at Y is 85°. The sketch writes 180° along the straight line. How many degrees is the outside angle at Y?

   95
6. 6.

   Pia draws triangle SUV and extends side SU past corner U. Angle S is 42° and angle V is 58°. How many degrees is the outside angle at U?

   100
8. 7.

   Ari cuts three copies of a 50°-60°-70° triangle and puts the three different corners side by side along a ruler. What do the three corners make together?

   • A straight line: 180°
   • A full turn around a point: 360°
   • A square corner: 90°
9. 8.

   Bo cuts three copies of a 35°-55°-90° triangle and puts the three different corners side by side along a ruler. What do the three corners make together?

   Use the picture in question 7.

   • A full turn: 360°
   • A straight line: 180°
   • A square corner, like a book corner: 90°
10. 9.

    Esme cuts three copies of a 30°-40°-110° triangle and puts the three different corners side by side along a ruler. What do the three corners make together?

    Use the picture in question 7.

    • A full circle around one point: 360°
    • A straight line: 180°
    • A square corner: 90°
11. 10.

    Jun cuts three copies of a 40°-70°-70° triangle and puts the three different corners side by side along a ruler. What do the three corners make together?

    Use the picture in question 7.

    • A square corner: 90°
    • A straight line: 180°
    • A full turn: 360°