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.

   Ari measures a triangular sail. Two of its angles are 47° and 68°. The sketch writes 180° beside the triangle. What is the third angle?

   65
2. 2.

   Esme measures a triangular tent flap. Two of its angles are 35° and 73°. The sketch writes 180° beside the triangle. What is the third angle?

   72
3. 3.

   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
4. 4.

   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
5. 5.

   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
6. 6.

   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
7. 7.

   Ren draws triangle WYC and extends side WY past corner Y. Angle W is 36° and angle C is 49°. How many degrees is the outside angle at Y?

   85
8. 8.

   Tala draws triangle DFG and extends side DF past corner F. Angle D is 57° and angle G is 29°. How many degrees is the outside angle at F?

   86
9. 9.

   Zee draws triangle HQS and extends side HQ past corner Q. Angle H is 44° and angle S is 71°. How many degrees is the outside angle at Q?

   115
10. 10.

    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?

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