ReasoningAges 13-15

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 13-15

Missing triangle angles

Take your time. Show your thinking.

1. Two interior angles of a triangle measure 61° and 27°. Find the third angle.
61° · 27° · Missing triangle angles
2. Two interior angles of a triangle measure 44° and 25°. Find the third angle.
44° · 25° · Missing triangle angles
3. Two interior angles of a triangle measure 68° and 40°. Find the third angle.
68° · 40° · Missing triangle angles
4. Two interior angles of a triangle measure 31° and 50°. Find the third angle.
31° · 50° · Missing triangle angles
5. Two interior angles of a triangle measure 77° and 47°. Find the third angle.
77° · 47° · Missing triangle angles
6. Two interior angles of a triangle measure 54° and 56°. Find the third angle.
54° · 56° · Missing triangle angles
7. Two interior angles of a triangle measure 84° and 27°. Find the third angle.
84° · 27° · Missing triangle angles
8. Two interior angles of a triangle measure 33° and 74°. Find the third angle.
33° · 74° · Missing triangle angles
9. Two interior angles of a triangle measure 36° and 49°. Find the third angle.
36° · 49° · Missing triangle angles
10. Two interior angles of a triangle measure 37° and 47°. Find the third angle.
37° · 47° · Missing triangle angles
11. Two interior angles of a triangle measure 60° and 37°. Find the third angle.
60° · 37° · Missing triangle angles
12. Two interior angles of a triangle measure 68° and 26°. Find the third angle.
68° · 26° · Missing triangle angles

12 questions · Seed 43 · Age guidance, not curriculum certification

View the answer key

Worksheet StudioAnswer key · Ages 13-15

Missing triangle angles

Answers and reasoning. Review before teaching.

1. Two interior angles of a triangle measure 61° and 27°. Find the third angle.
92°
Angles in a triangle sum to 180°: 180° − (61° + 27°) = 92°.
2. Two interior angles of a triangle measure 44° and 25°. Find the third angle.
111°
Angles in a triangle sum to 180°: 180° − (44° + 25°) = 111°.
3. Two interior angles of a triangle measure 68° and 40°. Find the third angle.
72°
Angles in a triangle sum to 180°: 180° − (68° + 40°) = 72°.
4. Two interior angles of a triangle measure 31° and 50°. Find the third angle.
99°
Angles in a triangle sum to 180°: 180° − (31° + 50°) = 99°.
5. Two interior angles of a triangle measure 77° and 47°. Find the third angle.
56°
Angles in a triangle sum to 180°: 180° − (77° + 47°) = 56°.
6. Two interior angles of a triangle measure 54° and 56°. Find the third angle.
70°
Angles in a triangle sum to 180°: 180° − (54° + 56°) = 70°.
7. Two interior angles of a triangle measure 84° and 27°. Find the third angle.
69°
Angles in a triangle sum to 180°: 180° − (84° + 27°) = 69°.
8. Two interior angles of a triangle measure 33° and 74°. Find the third angle.
73°
Angles in a triangle sum to 180°: 180° − (33° + 74°) = 73°.
9. Two interior angles of a triangle measure 36° and 49°. Find the third angle.
95°
Angles in a triangle sum to 180°: 180° − (36° + 49°) = 95°.
10. Two interior angles of a triangle measure 37° and 47°. Find the third angle.
96°
Angles in a triangle sum to 180°: 180° − (37° + 47°) = 96°.
11. Two interior angles of a triangle measure 60° and 37°. Find the third angle.
83°
Angles in a triangle sum to 180°: 180° − (60° + 37°) = 83°.
12. Two interior angles of a triangle measure 68° and 26°. Find the third angle.
86°
Angles in a triangle sum to 180°: 180° − (68° + 26°) = 86°.

12 questions · Seed 43 · Age guidance, not curriculum certification

Worksheet StudioPractice pack · Ages 13-15

Missing triangle angles

Take your time. Show your thinking.

1. Two interior angles of a triangle measure 61° and 27°. Find the third angle.
61° · 27° · Missing triangle angles
2. Two interior angles of a triangle measure 44° and 25°. Find the third angle.
44° · 25° · Missing triangle angles
3. Two interior angles of a triangle measure 68° and 40°. Find the third angle.
68° · 40° · Missing triangle angles
4. Two interior angles of a triangle measure 31° and 50°. Find the third angle.
31° · 50° · Missing triangle angles
5. Two interior angles of a triangle measure 77° and 47°. Find the third angle.
77° · 47° · Missing triangle angles
6. Two interior angles of a triangle measure 54° and 56°. Find the third angle.
54° · 56° · Missing triangle angles
7. Two interior angles of a triangle measure 84° and 27°. Find the third angle.
84° · 27° · Missing triangle angles
8. Two interior angles of a triangle measure 33° and 74°. Find the third angle.
33° · 74° · Missing triangle angles
9. Two interior angles of a triangle measure 36° and 49°. Find the third angle.
36° · 49° · Missing triangle angles
10. Two interior angles of a triangle measure 37° and 47°. Find the third angle.
37° · 47° · Missing triangle angles
11. Two interior angles of a triangle measure 60° and 37°. Find the third angle.
60° · 37° · Missing triangle angles
12. Two interior angles of a triangle measure 68° and 26°. Find the third angle.
68° · 26° · Missing triangle angles

12 questions · Seed 43 · Age guidance, not curriculum certification

Worksheet StudioAnswer key · Ages 13-15

Missing triangle angles

Answers and reasoning. Review before teaching.

1. Two interior angles of a triangle measure 61° and 27°. Find the third angle.
92°
Angles in a triangle sum to 180°: 180° − (61° + 27°) = 92°.
2. Two interior angles of a triangle measure 44° and 25°. Find the third angle.
111°
Angles in a triangle sum to 180°: 180° − (44° + 25°) = 111°.
3. Two interior angles of a triangle measure 68° and 40°. Find the third angle.
72°
Angles in a triangle sum to 180°: 180° − (68° + 40°) = 72°.
4. Two interior angles of a triangle measure 31° and 50°. Find the third angle.
99°
Angles in a triangle sum to 180°: 180° − (31° + 50°) = 99°.
5. Two interior angles of a triangle measure 77° and 47°. Find the third angle.
56°
Angles in a triangle sum to 180°: 180° − (77° + 47°) = 56°.
6. Two interior angles of a triangle measure 54° and 56°. Find the third angle.
70°
Angles in a triangle sum to 180°: 180° − (54° + 56°) = 70°.
7. Two interior angles of a triangle measure 84° and 27°. Find the third angle.
69°
Angles in a triangle sum to 180°: 180° − (84° + 27°) = 69°.
8. Two interior angles of a triangle measure 33° and 74°. Find the third angle.
73°
Angles in a triangle sum to 180°: 180° − (33° + 74°) = 73°.
9. Two interior angles of a triangle measure 36° and 49°. Find the third angle.
95°
Angles in a triangle sum to 180°: 180° − (36° + 49°) = 95°.
10. Two interior angles of a triangle measure 37° and 47°. Find the third angle.
96°
Angles in a triangle sum to 180°: 180° − (37° + 47°) = 96°.
11. Two interior angles of a triangle measure 60° and 37°. Find the third angle.
83°
Angles in a triangle sum to 180°: 180° − (60° + 37°) = 83°.
12. Two interior angles of a triangle measure 68° and 26°. Find the third angle.
86°
Angles in a triangle sum to 180°: 180° − (68° + 26°) = 86°.

12 questions · Seed 43 · Age guidance, not curriculum certification