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 83° and 47°. Find the third angle.
83° · 47° · Missing triangle angles
2. Two interior angles of a triangle measure 27° and 34°. Find the third angle.
27° · 34° · Missing triangle angles
3. Two interior angles of a triangle measure 26° and 34°. Find the third angle.
26° · 34° · Missing triangle angles
4. Two interior angles of a triangle measure 67° and 57°. Find the third angle.
67° · 57° · Missing triangle angles
5. Two interior angles of a triangle measure 76° and 45°. Find the third angle.
76° · 45° · Missing triangle angles
6. Two interior angles of a triangle measure 50° and 56°. Find the third angle.
50° · 56° · Missing triangle angles
7. Two interior angles of a triangle measure 31° and 66°. Find the third angle.
31° · 66° · Missing triangle angles
8. Two interior angles of a triangle measure 66° and 35°. Find the third angle.
66° · 35° · Missing triangle angles
9. Two interior angles of a triangle measure 32° and 30°. Find the third angle.
32° · 30° · Missing triangle angles
10. Two interior angles of a triangle measure 35° and 46°. Find the third angle.
35° · 46° · Missing triangle angles
11. Two interior angles of a triangle measure 58° and 26°. Find the third angle.
58° · 26° · Missing triangle angles
12. Two interior angles of a triangle measure 61° and 50°. Find the third angle.
61° · 50° · Missing triangle angles

12 questions · Seed 49 · 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 83° and 47°. Find the third angle.
50°
Angles in a triangle sum to 180°: 180° − (83° + 47°) = 50°.
2. Two interior angles of a triangle measure 27° and 34°. Find the third angle.
119°
Angles in a triangle sum to 180°: 180° − (27° + 34°) = 119°.
3. Two interior angles of a triangle measure 26° and 34°. Find the third angle.
120°
Angles in a triangle sum to 180°: 180° − (26° + 34°) = 120°.
4. Two interior angles of a triangle measure 67° and 57°. Find the third angle.
56°
Angles in a triangle sum to 180°: 180° − (67° + 57°) = 56°.
5. Two interior angles of a triangle measure 76° and 45°. Find the third angle.
59°
Angles in a triangle sum to 180°: 180° − (76° + 45°) = 59°.
6. Two interior angles of a triangle measure 50° and 56°. Find the third angle.
74°
Angles in a triangle sum to 180°: 180° − (50° + 56°) = 74°.
7. Two interior angles of a triangle measure 31° and 66°. Find the third angle.
83°
Angles in a triangle sum to 180°: 180° − (31° + 66°) = 83°.
8. Two interior angles of a triangle measure 66° and 35°. Find the third angle.
79°
Angles in a triangle sum to 180°: 180° − (66° + 35°) = 79°.
9. Two interior angles of a triangle measure 32° and 30°. Find the third angle.
118°
Angles in a triangle sum to 180°: 180° − (32° + 30°) = 118°.
10. Two interior angles of a triangle measure 35° and 46°. Find the third angle.
99°
Angles in a triangle sum to 180°: 180° − (35° + 46°) = 99°.
11. Two interior angles of a triangle measure 58° and 26°. Find the third angle.
96°
Angles in a triangle sum to 180°: 180° − (58° + 26°) = 96°.
12. Two interior angles of a triangle measure 61° and 50°. Find the third angle.
69°
Angles in a triangle sum to 180°: 180° − (61° + 50°) = 69°.

12 questions · Seed 49 · 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 83° and 47°. Find the third angle.
83° · 47° · Missing triangle angles
2. Two interior angles of a triangle measure 27° and 34°. Find the third angle.
27° · 34° · Missing triangle angles
3. Two interior angles of a triangle measure 26° and 34°. Find the third angle.
26° · 34° · Missing triangle angles
4. Two interior angles of a triangle measure 67° and 57°. Find the third angle.
67° · 57° · Missing triangle angles
5. Two interior angles of a triangle measure 76° and 45°. Find the third angle.
76° · 45° · Missing triangle angles
6. Two interior angles of a triangle measure 50° and 56°. Find the third angle.
50° · 56° · Missing triangle angles
7. Two interior angles of a triangle measure 31° and 66°. Find the third angle.
31° · 66° · Missing triangle angles
8. Two interior angles of a triangle measure 66° and 35°. Find the third angle.
66° · 35° · Missing triangle angles
9. Two interior angles of a triangle measure 32° and 30°. Find the third angle.
32° · 30° · Missing triangle angles
10. Two interior angles of a triangle measure 35° and 46°. Find the third angle.
35° · 46° · Missing triangle angles
11. Two interior angles of a triangle measure 58° and 26°. Find the third angle.
58° · 26° · Missing triangle angles
12. Two interior angles of a triangle measure 61° and 50°. Find the third angle.
61° · 50° · Missing triangle angles

12 questions · Seed 49 · 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 83° and 47°. Find the third angle.
50°
Angles in a triangle sum to 180°: 180° − (83° + 47°) = 50°.
2. Two interior angles of a triangle measure 27° and 34°. Find the third angle.
119°
Angles in a triangle sum to 180°: 180° − (27° + 34°) = 119°.
3. Two interior angles of a triangle measure 26° and 34°. Find the third angle.
120°
Angles in a triangle sum to 180°: 180° − (26° + 34°) = 120°.
4. Two interior angles of a triangle measure 67° and 57°. Find the third angle.
56°
Angles in a triangle sum to 180°: 180° − (67° + 57°) = 56°.
5. Two interior angles of a triangle measure 76° and 45°. Find the third angle.
59°
Angles in a triangle sum to 180°: 180° − (76° + 45°) = 59°.
6. Two interior angles of a triangle measure 50° and 56°. Find the third angle.
74°
Angles in a triangle sum to 180°: 180° − (50° + 56°) = 74°.
7. Two interior angles of a triangle measure 31° and 66°. Find the third angle.
83°
Angles in a triangle sum to 180°: 180° − (31° + 66°) = 83°.
8. Two interior angles of a triangle measure 66° and 35°. Find the third angle.
79°
Angles in a triangle sum to 180°: 180° − (66° + 35°) = 79°.
9. Two interior angles of a triangle measure 32° and 30°. Find the third angle.
118°
Angles in a triangle sum to 180°: 180° − (32° + 30°) = 118°.
10. Two interior angles of a triangle measure 35° and 46°. Find the third angle.
99°
Angles in a triangle sum to 180°: 180° − (35° + 46°) = 99°.
11. Two interior angles of a triangle measure 58° and 26°. Find the third angle.
96°
Angles in a triangle sum to 180°: 180° − (58° + 26°) = 96°.
12. Two interior angles of a triangle measure 61° and 50°. Find the third angle.
69°
Angles in a triangle sum to 180°: 180° − (61° + 50°) = 69°.

12 questions · Seed 49 · Age guidance, not curriculum certification