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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 47° and 66°. Find the third angle.

    47° · 66° · Missing triangle angles

  2. 2. Two interior angles of a triangle measure 69° and 65°. Find the third angle.

    69° · 65° · Missing triangle angles

  3. 3. Two interior angles of a triangle measure 76° and 71°. Find the third angle.

    76° · 71° · Missing triangle angles

  4. 4. Two interior angles of a triangle measure 29° and 44°. Find the third angle.

    29° · 44° · Missing triangle angles

  5. 5. Two interior angles of a triangle measure 38° and 64°. Find the third angle.

    38° · 64° · Missing triangle angles

  6. 6. Two interior angles of a triangle measure 41° and 46°. Find the third angle.

    41° · 46° · Missing triangle angles

  7. 7. Two interior angles of a triangle measure 45° and 28°. Find the third angle.

    45° · 28° · Missing triangle angles

  8. 8. Two interior angles of a triangle measure 45° and 36°. Find the third angle.

    45° · 36° · Missing triangle angles

  9. 9. Two interior angles of a triangle measure 28° and 43°. Find the third angle.

    28° · 43° · Missing triangle angles

  10. 10. Two interior angles of a triangle measure 26° and 60°. Find the third angle.

    26° · 60° · Missing triangle angles

  11. 11. Two interior angles of a triangle measure 64° and 68°. Find the third angle.

    64° · 68° · Missing triangle angles

  12. 12. Two interior angles of a triangle measure 39° and 57°. Find the third angle.

    39° · 57° · Missing triangle angles
12 questions · Seed 50 · 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 47° and 66°. Find the third angle.

    67°

    Angles in a triangle sum to 180°: 180° − (47° + 66°) = 67°.

  2. 2. Two interior angles of a triangle measure 69° and 65°. Find the third angle.

    46°

    Angles in a triangle sum to 180°: 180° − (69° + 65°) = 46°.

  3. 3. Two interior angles of a triangle measure 76° and 71°. Find the third angle.

    33°

    Angles in a triangle sum to 180°: 180° − (76° + 71°) = 33°.

  4. 4. Two interior angles of a triangle measure 29° and 44°. Find the third angle.

    107°

    Angles in a triangle sum to 180°: 180° − (29° + 44°) = 107°.

  5. 5. Two interior angles of a triangle measure 38° and 64°. Find the third angle.

    78°

    Angles in a triangle sum to 180°: 180° − (38° + 64°) = 78°.

  6. 6. Two interior angles of a triangle measure 41° and 46°. Find the third angle.

    93°

    Angles in a triangle sum to 180°: 180° − (41° + 46°) = 93°.

  7. 7. Two interior angles of a triangle measure 45° and 28°. Find the third angle.

    107°

    Angles in a triangle sum to 180°: 180° − (45° + 28°) = 107°.

  8. 8. Two interior angles of a triangle measure 45° and 36°. Find the third angle.

    99°

    Angles in a triangle sum to 180°: 180° − (45° + 36°) = 99°.

  9. 9. Two interior angles of a triangle measure 28° and 43°. Find the third angle.

    109°

    Angles in a triangle sum to 180°: 180° − (28° + 43°) = 109°.

  10. 10. Two interior angles of a triangle measure 26° and 60°. Find the third angle.

    94°

    Angles in a triangle sum to 180°: 180° − (26° + 60°) = 94°.

  11. 11. Two interior angles of a triangle measure 64° and 68°. Find the third angle.

    48°

    Angles in a triangle sum to 180°: 180° − (64° + 68°) = 48°.

  12. 12. Two interior angles of a triangle measure 39° and 57°. Find the third angle.

    84°

    Angles in a triangle sum to 180°: 180° − (39° + 57°) = 84°.

12 questions · Seed 50 · 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 47° and 66°. Find the third angle.

    47° · 66° · Missing triangle angles

  2. 2. Two interior angles of a triangle measure 69° and 65°. Find the third angle.

    69° · 65° · Missing triangle angles

  3. 3. Two interior angles of a triangle measure 76° and 71°. Find the third angle.

    76° · 71° · Missing triangle angles

  4. 4. Two interior angles of a triangle measure 29° and 44°. Find the third angle.

    29° · 44° · Missing triangle angles

  5. 5. Two interior angles of a triangle measure 38° and 64°. Find the third angle.

    38° · 64° · Missing triangle angles

  6. 6. Two interior angles of a triangle measure 41° and 46°. Find the third angle.

    41° · 46° · Missing triangle angles

  7. 7. Two interior angles of a triangle measure 45° and 28°. Find the third angle.

    45° · 28° · Missing triangle angles

  8. 8. Two interior angles of a triangle measure 45° and 36°. Find the third angle.

    45° · 36° · Missing triangle angles

  9. 9. Two interior angles of a triangle measure 28° and 43°. Find the third angle.

    28° · 43° · Missing triangle angles

  10. 10. Two interior angles of a triangle measure 26° and 60°. Find the third angle.

    26° · 60° · Missing triangle angles

  11. 11. Two interior angles of a triangle measure 64° and 68°. Find the third angle.

    64° · 68° · Missing triangle angles

  12. 12. Two interior angles of a triangle measure 39° and 57°. Find the third angle.

    39° · 57° · Missing triangle angles
12 questions · Seed 50 · 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 47° and 66°. Find the third angle.

    67°

    Angles in a triangle sum to 180°: 180° − (47° + 66°) = 67°.

  2. 2. Two interior angles of a triangle measure 69° and 65°. Find the third angle.

    46°

    Angles in a triangle sum to 180°: 180° − (69° + 65°) = 46°.

  3. 3. Two interior angles of a triangle measure 76° and 71°. Find the third angle.

    33°

    Angles in a triangle sum to 180°: 180° − (76° + 71°) = 33°.

  4. 4. Two interior angles of a triangle measure 29° and 44°. Find the third angle.

    107°

    Angles in a triangle sum to 180°: 180° − (29° + 44°) = 107°.

  5. 5. Two interior angles of a triangle measure 38° and 64°. Find the third angle.

    78°

    Angles in a triangle sum to 180°: 180° − (38° + 64°) = 78°.

  6. 6. Two interior angles of a triangle measure 41° and 46°. Find the third angle.

    93°

    Angles in a triangle sum to 180°: 180° − (41° + 46°) = 93°.

  7. 7. Two interior angles of a triangle measure 45° and 28°. Find the third angle.

    107°

    Angles in a triangle sum to 180°: 180° − (45° + 28°) = 107°.

  8. 8. Two interior angles of a triangle measure 45° and 36°. Find the third angle.

    99°

    Angles in a triangle sum to 180°: 180° − (45° + 36°) = 99°.

  9. 9. Two interior angles of a triangle measure 28° and 43°. Find the third angle.

    109°

    Angles in a triangle sum to 180°: 180° − (28° + 43°) = 109°.

  10. 10. Two interior angles of a triangle measure 26° and 60°. Find the third angle.

    94°

    Angles in a triangle sum to 180°: 180° − (26° + 60°) = 94°.

  11. 11. Two interior angles of a triangle measure 64° and 68°. Find the third angle.

    48°

    Angles in a triangle sum to 180°: 180° − (64° + 68°) = 48°.

  12. 12. Two interior angles of a triangle measure 39° and 57°. Find the third angle.

    84°

    Angles in a triangle sum to 180°: 180° − (39° + 57°) = 84°.

12 questions · Seed 50 · Age guidance, not curriculum certification