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ReasoningAges 10-12

Missing triangle angles

Use the 180° interior angle sum of a triangle to deduce an unknown angle. Review suitability for your learners before teaching.

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Age band:Ages 10-12Ages 13-15

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Worksheet StudioPractice pack · Ages 10-12

Missing triangle angles

Take your time. Show your thinking.

  1. 1. Two interior angles of a triangle measure 64° and 65°. Find the third angle.

    64° · 65° · Missing triangle angles

  2. 2. Two interior angles of a triangle measure 26° and 54°. Find the third angle.

    26° · 54° · Missing triangle angles

  3. 3. Two interior angles of a triangle measure 43° and 69°. Find the third angle.

    43° · 69° · Missing triangle angles

  4. 4. Two interior angles of a triangle measure 32° and 25°. Find the third angle.

    32° · 25° · Missing triangle angles

  5. 5. Two interior angles of a triangle measure 38° and 46°. Find the third angle.

    38° · 46° · Missing triangle angles

  6. 6. Two interior angles of a triangle measure 81° and 72°. Find the third angle.

    81° · 72° · Missing triangle angles

  7. 7. Two interior angles of a triangle measure 25° and 40°. Find the third angle.

    25° · 40° · Missing triangle angles

  8. 8. Two interior angles of a triangle measure 31° and 57°. Find the third angle.

    31° · 57° · Missing triangle angles

  9. 9. Two interior angles of a triangle measure 39° and 62°. Find the third angle.

    39° · 62° · Missing triangle angles

  10. 10. Two interior angles of a triangle measure 36° and 29°. Find the third angle.

    36° · 29° · Missing triangle angles

  11. 11. Two interior angles of a triangle measure 43° and 57°. Find the third angle.

    43° · 57° · Missing triangle angles

  12. 12. Two interior angles of a triangle measure 80° and 59°. Find the third angle.

    80° · 59° · Missing triangle angles
12 questions · Seed 104731 · Age guidance, not curriculum certification
View the answer key
Worksheet StudioAnswer key · Ages 10-12

Missing triangle angles

Answers and reasoning. Review before teaching.

  1. 1. Two interior angles of a triangle measure 64° and 65°. Find the third angle.

    51°

    Angles in a triangle sum to 180°: 180° − (64° + 65°) = 51°.

  2. 2. Two interior angles of a triangle measure 26° and 54°. Find the third angle.

    100°

    Angles in a triangle sum to 180°: 180° − (26° + 54°) = 100°.

  3. 3. Two interior angles of a triangle measure 43° and 69°. Find the third angle.

    68°

    Angles in a triangle sum to 180°: 180° − (43° + 69°) = 68°.

  4. 4. Two interior angles of a triangle measure 32° and 25°. Find the third angle.

    123°

    Angles in a triangle sum to 180°: 180° − (32° + 25°) = 123°.

  5. 5. Two interior angles of a triangle measure 38° and 46°. Find the third angle.

    96°

    Angles in a triangle sum to 180°: 180° − (38° + 46°) = 96°.

  6. 6. Two interior angles of a triangle measure 81° and 72°. Find the third angle.

    27°

    Angles in a triangle sum to 180°: 180° − (81° + 72°) = 27°.

  7. 7. Two interior angles of a triangle measure 25° and 40°. Find the third angle.

    115°

    Angles in a triangle sum to 180°: 180° − (25° + 40°) = 115°.

  8. 8. Two interior angles of a triangle measure 31° and 57°. Find the third angle.

    92°

    Angles in a triangle sum to 180°: 180° − (31° + 57°) = 92°.

  9. 9. Two interior angles of a triangle measure 39° and 62°. Find the third angle.

    79°

    Angles in a triangle sum to 180°: 180° − (39° + 62°) = 79°.

  10. 10. Two interior angles of a triangle measure 36° and 29°. Find the third angle.

    115°

    Angles in a triangle sum to 180°: 180° − (36° + 29°) = 115°.

  11. 11. Two interior angles of a triangle measure 43° and 57°. Find the third angle.

    80°

    Angles in a triangle sum to 180°: 180° − (43° + 57°) = 80°.

  12. 12. Two interior angles of a triangle measure 80° and 59°. Find the third angle.

    41°

    Angles in a triangle sum to 180°: 180° − (80° + 59°) = 41°.

12 questions · Seed 104731 · Age guidance, not curriculum certification
Worksheet StudioPractice pack · Ages 10-12

Missing triangle angles

Take your time. Show your thinking.

  1. 1. Two interior angles of a triangle measure 64° and 65°. Find the third angle.

    64° · 65° · Missing triangle angles

  2. 2. Two interior angles of a triangle measure 26° and 54°. Find the third angle.

    26° · 54° · Missing triangle angles

  3. 3. Two interior angles of a triangle measure 43° and 69°. Find the third angle.

    43° · 69° · Missing triangle angles

  4. 4. Two interior angles of a triangle measure 32° and 25°. Find the third angle.

    32° · 25° · Missing triangle angles

  5. 5. Two interior angles of a triangle measure 38° and 46°. Find the third angle.

    38° · 46° · Missing triangle angles

  6. 6. Two interior angles of a triangle measure 81° and 72°. Find the third angle.

    81° · 72° · Missing triangle angles

  7. 7. Two interior angles of a triangle measure 25° and 40°. Find the third angle.

    25° · 40° · Missing triangle angles

  8. 8. Two interior angles of a triangle measure 31° and 57°. Find the third angle.

    31° · 57° · Missing triangle angles

  9. 9. Two interior angles of a triangle measure 39° and 62°. Find the third angle.

    39° · 62° · Missing triangle angles

  10. 10. Two interior angles of a triangle measure 36° and 29°. Find the third angle.

    36° · 29° · Missing triangle angles

  11. 11. Two interior angles of a triangle measure 43° and 57°. Find the third angle.

    43° · 57° · Missing triangle angles

  12. 12. Two interior angles of a triangle measure 80° and 59°. Find the third angle.

    80° · 59° · Missing triangle angles
12 questions · Seed 104731 · Age guidance, not curriculum certification
Worksheet StudioAnswer key · Ages 10-12

Missing triangle angles

Answers and reasoning. Review before teaching.

  1. 1. Two interior angles of a triangle measure 64° and 65°. Find the third angle.

    51°

    Angles in a triangle sum to 180°: 180° − (64° + 65°) = 51°.

  2. 2. Two interior angles of a triangle measure 26° and 54°. Find the third angle.

    100°

    Angles in a triangle sum to 180°: 180° − (26° + 54°) = 100°.

  3. 3. Two interior angles of a triangle measure 43° and 69°. Find the third angle.

    68°

    Angles in a triangle sum to 180°: 180° − (43° + 69°) = 68°.

  4. 4. Two interior angles of a triangle measure 32° and 25°. Find the third angle.

    123°

    Angles in a triangle sum to 180°: 180° − (32° + 25°) = 123°.

  5. 5. Two interior angles of a triangle measure 38° and 46°. Find the third angle.

    96°

    Angles in a triangle sum to 180°: 180° − (38° + 46°) = 96°.

  6. 6. Two interior angles of a triangle measure 81° and 72°. Find the third angle.

    27°

    Angles in a triangle sum to 180°: 180° − (81° + 72°) = 27°.

  7. 7. Two interior angles of a triangle measure 25° and 40°. Find the third angle.

    115°

    Angles in a triangle sum to 180°: 180° − (25° + 40°) = 115°.

  8. 8. Two interior angles of a triangle measure 31° and 57°. Find the third angle.

    92°

    Angles in a triangle sum to 180°: 180° − (31° + 57°) = 92°.

  9. 9. Two interior angles of a triangle measure 39° and 62°. Find the third angle.

    79°

    Angles in a triangle sum to 180°: 180° − (39° + 62°) = 79°.

  10. 10. Two interior angles of a triangle measure 36° and 29°. Find the third angle.

    115°

    Angles in a triangle sum to 180°: 180° − (36° + 29°) = 115°.

  11. 11. Two interior angles of a triangle measure 43° and 57°. Find the third angle.

    80°

    Angles in a triangle sum to 180°: 180° − (43° + 57°) = 80°.

  12. 12. Two interior angles of a triangle measure 80° and 59°. Find the third angle.

    41°

    Angles in a triangle sum to 180°: 180° − (80° + 59°) = 41°.

12 questions · Seed 104731 · Age guidance, not curriculum certification