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 10-12 Ages 13-15

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Worksheet StudioPractice pack · Ages 10-12

Missing triangle angles

Take your time. Show your thinking.

1. Two interior angles of a triangle measure 68° and 52°. Find the third angle.
68° · 52° · Missing triangle angles
2. Two interior angles of a triangle measure 70° and 61°. Find the third angle.
70° · 61° · Missing triangle angles
3. Two interior angles of a triangle measure 57° and 64°. Find the third angle.
57° · 64° · Missing triangle angles
4. Two interior angles of a triangle measure 41° and 50°. Find the third angle.
41° · 50° · Missing triangle angles
5. Two interior angles of a triangle measure 69° and 25°. Find the third angle.
69° · 25° · Missing triangle angles
6. Two interior angles of a triangle measure 83° and 37°. Find the third angle.
83° · 37° · Missing triangle angles
7. Two interior angles of a triangle measure 46° and 41°. Find the third angle.
46° · 41° · Missing triangle angles
8. Two interior angles of a triangle measure 85° and 31°. Find the third angle.
85° · 31° · Missing triangle angles
9. Two interior angles of a triangle measure 48° and 48°. Find the third angle.
48° · 48° · Missing triangle angles
10. Two interior angles of a triangle measure 38° and 25°. Find the third angle.
38° · 25° · Missing triangle angles
11. Two interior angles of a triangle measure 38° and 55°. Find the third angle.
38° · 55° · Missing triangle angles
12. Two interior angles of a triangle measure 54° and 50°. Find the third angle.
54° · 50° · Missing triangle angles

12 questions · Seed 65 · 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. Two interior angles of a triangle measure 68° and 52°. Find the third angle.
60°
Angles in a triangle sum to 180°: 180° − (68° + 52°) = 60°.
2. Two interior angles of a triangle measure 70° and 61°. Find the third angle.
49°
Angles in a triangle sum to 180°: 180° − (70° + 61°) = 49°.
3. Two interior angles of a triangle measure 57° and 64°. Find the third angle.
59°
Angles in a triangle sum to 180°: 180° − (57° + 64°) = 59°.
4. Two interior angles of a triangle measure 41° and 50°. Find the third angle.
89°
Angles in a triangle sum to 180°: 180° − (41° + 50°) = 89°.
5. Two interior angles of a triangle measure 69° and 25°. Find the third angle.
86°
Angles in a triangle sum to 180°: 180° − (69° + 25°) = 86°.
6. Two interior angles of a triangle measure 83° and 37°. Find the third angle.
60°
Angles in a triangle sum to 180°: 180° − (83° + 37°) = 60°.
7. Two interior angles of a triangle measure 46° and 41°. Find the third angle.
93°
Angles in a triangle sum to 180°: 180° − (46° + 41°) = 93°.
8. Two interior angles of a triangle measure 85° and 31°. Find the third angle.
64°
Angles in a triangle sum to 180°: 180° − (85° + 31°) = 64°.
9. Two interior angles of a triangle measure 48° and 48°. Find the third angle.
84°
Angles in a triangle sum to 180°: 180° − (48° + 48°) = 84°.
10. Two interior angles of a triangle measure 38° and 25°. Find the third angle.
117°
Angles in a triangle sum to 180°: 180° − (38° + 25°) = 117°.
11. Two interior angles of a triangle measure 38° and 55°. Find the third angle.
87°
Angles in a triangle sum to 180°: 180° − (38° + 55°) = 87°.
12. Two interior angles of a triangle measure 54° and 50°. Find the third angle.
76°
Angles in a triangle sum to 180°: 180° − (54° + 50°) = 76°.

12 questions · Seed 65 · Age guidance, not curriculum certification

Worksheet StudioPractice pack · Ages 10-12

Missing triangle angles

Take your time. Show your thinking.

1. Two interior angles of a triangle measure 68° and 52°. Find the third angle.
68° · 52° · Missing triangle angles
2. Two interior angles of a triangle measure 70° and 61°. Find the third angle.
70° · 61° · Missing triangle angles
3. Two interior angles of a triangle measure 57° and 64°. Find the third angle.
57° · 64° · Missing triangle angles
4. Two interior angles of a triangle measure 41° and 50°. Find the third angle.
41° · 50° · Missing triangle angles
5. Two interior angles of a triangle measure 69° and 25°. Find the third angle.
69° · 25° · Missing triangle angles
6. Two interior angles of a triangle measure 83° and 37°. Find the third angle.
83° · 37° · Missing triangle angles
7. Two interior angles of a triangle measure 46° and 41°. Find the third angle.
46° · 41° · Missing triangle angles
8. Two interior angles of a triangle measure 85° and 31°. Find the third angle.
85° · 31° · Missing triangle angles
9. Two interior angles of a triangle measure 48° and 48°. Find the third angle.
48° · 48° · Missing triangle angles
10. Two interior angles of a triangle measure 38° and 25°. Find the third angle.
38° · 25° · Missing triangle angles
11. Two interior angles of a triangle measure 38° and 55°. Find the third angle.
38° · 55° · Missing triangle angles
12. Two interior angles of a triangle measure 54° and 50°. Find the third angle.
54° · 50° · Missing triangle angles

12 questions · Seed 65 · Age guidance, not curriculum certification

Worksheet StudioAnswer key · Ages 10-12

Missing triangle angles

Answers and reasoning. Review before teaching.

1. Two interior angles of a triangle measure 68° and 52°. Find the third angle.
60°
Angles in a triangle sum to 180°: 180° − (68° + 52°) = 60°.
2. Two interior angles of a triangle measure 70° and 61°. Find the third angle.
49°
Angles in a triangle sum to 180°: 180° − (70° + 61°) = 49°.
3. Two interior angles of a triangle measure 57° and 64°. Find the third angle.
59°
Angles in a triangle sum to 180°: 180° − (57° + 64°) = 59°.
4. Two interior angles of a triangle measure 41° and 50°. Find the third angle.
89°
Angles in a triangle sum to 180°: 180° − (41° + 50°) = 89°.
5. Two interior angles of a triangle measure 69° and 25°. Find the third angle.
86°
Angles in a triangle sum to 180°: 180° − (69° + 25°) = 86°.
6. Two interior angles of a triangle measure 83° and 37°. Find the third angle.
60°
Angles in a triangle sum to 180°: 180° − (83° + 37°) = 60°.
7. Two interior angles of a triangle measure 46° and 41°. Find the third angle.
93°
Angles in a triangle sum to 180°: 180° − (46° + 41°) = 93°.
8. Two interior angles of a triangle measure 85° and 31°. Find the third angle.
64°
Angles in a triangle sum to 180°: 180° − (85° + 31°) = 64°.
9. Two interior angles of a triangle measure 48° and 48°. Find the third angle.
84°
Angles in a triangle sum to 180°: 180° − (48° + 48°) = 84°.
10. Two interior angles of a triangle measure 38° and 25°. Find the third angle.
117°
Angles in a triangle sum to 180°: 180° − (38° + 25°) = 117°.
11. Two interior angles of a triangle measure 38° and 55°. Find the third angle.
87°
Angles in a triangle sum to 180°: 180° − (38° + 55°) = 87°.
12. Two interior angles of a triangle measure 54° and 50°. Find the third angle.
76°
Angles in a triangle sum to 180°: 180° − (54° + 50°) = 76°.

12 questions · Seed 65 · Age guidance, not curriculum certification