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 47° and 66°. Find the third angle.
47° · 66° · Missing triangle angles
2. Two interior angles of a triangle measure 69° and 63°. Find the third angle.
69° · 63° · Missing triangle angles
3. Two interior angles of a triangle measure 63° and 49°. Find the third angle.
63° · 49° · Missing triangle angles
4. Two interior angles of a triangle measure 75° and 40°. Find the third angle.
75° · 40° · Missing triangle angles
5. Two interior angles of a triangle measure 34° and 40°. Find the third angle.
34° · 40° · Missing triangle angles
6. Two interior angles of a triangle measure 43° and 68°. Find the third angle.
43° · 68° · Missing triangle angles
7. Two interior angles of a triangle measure 68° and 67°. Find the third angle.
68° · 67° · Missing triangle angles
8. Two interior angles of a triangle measure 55° and 53°. Find the third angle.
55° · 53° · Missing triangle angles
9. Two interior angles of a triangle measure 69° and 57°. Find the third angle.
69° · 57° · Missing triangle angles
10. Two interior angles of a triangle measure 54° and 34°. Find the third angle.
54° · 34° · Missing triangle angles
11. Two interior angles of a triangle measure 41° and 31°. Find the third angle.
41° · 31° · Missing triangle angles
12. Two interior angles of a triangle measure 44° and 39°. Find the third angle.
44° · 39° · Missing triangle angles

12 questions · Seed 104732 · 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 47° and 66°. Find the third angle.
67°
Angles in a triangle sum to 180°: 180° − (47° + 66°) = 67°.
2. Two interior angles of a triangle measure 69° and 63°. Find the third angle.
48°
Angles in a triangle sum to 180°: 180° − (69° + 63°) = 48°.
3. Two interior angles of a triangle measure 63° and 49°. Find the third angle.
68°
Angles in a triangle sum to 180°: 180° − (63° + 49°) = 68°.
4. Two interior angles of a triangle measure 75° and 40°. Find the third angle.
65°
Angles in a triangle sum to 180°: 180° − (75° + 40°) = 65°.
5. Two interior angles of a triangle measure 34° and 40°. Find the third angle.
106°
Angles in a triangle sum to 180°: 180° − (34° + 40°) = 106°.
6. Two interior angles of a triangle measure 43° and 68°. Find the third angle.
69°
Angles in a triangle sum to 180°: 180° − (43° + 68°) = 69°.
7. Two interior angles of a triangle measure 68° and 67°. Find the third angle.
45°
Angles in a triangle sum to 180°: 180° − (68° + 67°) = 45°.
8. Two interior angles of a triangle measure 55° and 53°. Find the third angle.
72°
Angles in a triangle sum to 180°: 180° − (55° + 53°) = 72°.
9. Two interior angles of a triangle measure 69° and 57°. Find the third angle.
54°
Angles in a triangle sum to 180°: 180° − (69° + 57°) = 54°.
10. Two interior angles of a triangle measure 54° and 34°. Find the third angle.
92°
Angles in a triangle sum to 180°: 180° − (54° + 34°) = 92°.
11. Two interior angles of a triangle measure 41° and 31°. Find the third angle.
108°
Angles in a triangle sum to 180°: 180° − (41° + 31°) = 108°.
12. Two interior angles of a triangle measure 44° and 39°. Find the third angle.
97°
Angles in a triangle sum to 180°: 180° − (44° + 39°) = 97°.

12 questions · Seed 104732 · 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 47° and 66°. Find the third angle.
47° · 66° · Missing triangle angles
2. Two interior angles of a triangle measure 69° and 63°. Find the third angle.
69° · 63° · Missing triangle angles
3. Two interior angles of a triangle measure 63° and 49°. Find the third angle.
63° · 49° · Missing triangle angles
4. Two interior angles of a triangle measure 75° and 40°. Find the third angle.
75° · 40° · Missing triangle angles
5. Two interior angles of a triangle measure 34° and 40°. Find the third angle.
34° · 40° · Missing triangle angles
6. Two interior angles of a triangle measure 43° and 68°. Find the third angle.
43° · 68° · Missing triangle angles
7. Two interior angles of a triangle measure 68° and 67°. Find the third angle.
68° · 67° · Missing triangle angles
8. Two interior angles of a triangle measure 55° and 53°. Find the third angle.
55° · 53° · Missing triangle angles
9. Two interior angles of a triangle measure 69° and 57°. Find the third angle.
69° · 57° · Missing triangle angles
10. Two interior angles of a triangle measure 54° and 34°. Find the third angle.
54° · 34° · Missing triangle angles
11. Two interior angles of a triangle measure 41° and 31°. Find the third angle.
41° · 31° · Missing triangle angles
12. Two interior angles of a triangle measure 44° and 39°. Find the third angle.
44° · 39° · Missing triangle angles

12 questions · Seed 104732 · 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 47° and 66°. Find the third angle.
67°
Angles in a triangle sum to 180°: 180° − (47° + 66°) = 67°.
2. Two interior angles of a triangle measure 69° and 63°. Find the third angle.
48°
Angles in a triangle sum to 180°: 180° − (69° + 63°) = 48°.
3. Two interior angles of a triangle measure 63° and 49°. Find the third angle.
68°
Angles in a triangle sum to 180°: 180° − (63° + 49°) = 68°.
4. Two interior angles of a triangle measure 75° and 40°. Find the third angle.
65°
Angles in a triangle sum to 180°: 180° − (75° + 40°) = 65°.
5. Two interior angles of a triangle measure 34° and 40°. Find the third angle.
106°
Angles in a triangle sum to 180°: 180° − (34° + 40°) = 106°.
6. Two interior angles of a triangle measure 43° and 68°. Find the third angle.
69°
Angles in a triangle sum to 180°: 180° − (43° + 68°) = 69°.
7. Two interior angles of a triangle measure 68° and 67°. Find the third angle.
45°
Angles in a triangle sum to 180°: 180° − (68° + 67°) = 45°.
8. Two interior angles of a triangle measure 55° and 53°. Find the third angle.
72°
Angles in a triangle sum to 180°: 180° − (55° + 53°) = 72°.
9. Two interior angles of a triangle measure 69° and 57°. Find the third angle.
54°
Angles in a triangle sum to 180°: 180° − (69° + 57°) = 54°.
10. Two interior angles of a triangle measure 54° and 34°. Find the third angle.
92°
Angles in a triangle sum to 180°: 180° − (54° + 34°) = 92°.
11. Two interior angles of a triangle measure 41° and 31°. Find the third angle.
108°
Angles in a triangle sum to 180°: 180° − (41° + 31°) = 108°.
12. Two interior angles of a triangle measure 44° and 39°. Find the third angle.
97°
Angles in a triangle sum to 180°: 180° − (44° + 39°) = 97°.

12 questions · Seed 104732 · Age guidance, not curriculum certification