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 33° and 63°. Find the third angle.
33° · 63° · Missing triangle angles
2. Two interior angles of a triangle measure 44° and 35°. Find the third angle.
44° · 35° · Missing triangle angles
3. Two interior angles of a triangle measure 83° and 73°. Find the third angle.
83° · 73° · Missing triangle angles
4. Two interior angles of a triangle measure 73° and 35°. Find the third angle.
73° · 35° · Missing triangle angles
5. Two interior angles of a triangle measure 53° and 46°. Find the third angle.
53° · 46° · Missing triangle angles
6. Two interior angles of a triangle measure 29° and 70°. Find the third angle.
29° · 70° · Missing triangle angles
7. Two interior angles of a triangle measure 78° and 61°. Find the third angle.
78° · 61° · Missing triangle angles
8. Two interior angles of a triangle measure 31° and 26°. Find the third angle.
31° · 26° · Missing triangle angles
9. Two interior angles of a triangle measure 30° and 28°. Find the third angle.
30° · 28° · Missing triangle angles
10. Two interior angles of a triangle measure 26° and 54°. Find the third angle.
26° · 54° · Missing triangle angles
11. Two interior angles of a triangle measure 51° and 27°. Find the third angle.
51° · 27° · Missing triangle angles
12. Two interior angles of a triangle measure 60° and 47°. Find the third angle.
60° · 47° · Missing triangle angles

12 questions · Seed 45 · 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 33° and 63°. Find the third angle.
84°
Angles in a triangle sum to 180°: 180° − (33° + 63°) = 84°.
2. Two interior angles of a triangle measure 44° and 35°. Find the third angle.
101°
Angles in a triangle sum to 180°: 180° − (44° + 35°) = 101°.
3. Two interior angles of a triangle measure 83° and 73°. Find the third angle.
24°
Angles in a triangle sum to 180°: 180° − (83° + 73°) = 24°.
4. Two interior angles of a triangle measure 73° and 35°. Find the third angle.
72°
Angles in a triangle sum to 180°: 180° − (73° + 35°) = 72°.
5. Two interior angles of a triangle measure 53° and 46°. Find the third angle.
81°
Angles in a triangle sum to 180°: 180° − (53° + 46°) = 81°.
6. Two interior angles of a triangle measure 29° and 70°. Find the third angle.
81°
Angles in a triangle sum to 180°: 180° − (29° + 70°) = 81°.
7. Two interior angles of a triangle measure 78° and 61°. Find the third angle.
41°
Angles in a triangle sum to 180°: 180° − (78° + 61°) = 41°.
8. Two interior angles of a triangle measure 31° and 26°. Find the third angle.
123°
Angles in a triangle sum to 180°: 180° − (31° + 26°) = 123°.
9. Two interior angles of a triangle measure 30° and 28°. Find the third angle.
122°
Angles in a triangle sum to 180°: 180° − (30° + 28°) = 122°.
10. Two interior angles of a triangle measure 26° and 54°. Find the third angle.
100°
Angles in a triangle sum to 180°: 180° − (26° + 54°) = 100°.
11. Two interior angles of a triangle measure 51° and 27°. Find the third angle.
102°
Angles in a triangle sum to 180°: 180° − (51° + 27°) = 102°.
12. Two interior angles of a triangle measure 60° and 47°. Find the third angle.
73°
Angles in a triangle sum to 180°: 180° − (60° + 47°) = 73°.

12 questions · Seed 45 · 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 33° and 63°. Find the third angle.
33° · 63° · Missing triangle angles
2. Two interior angles of a triangle measure 44° and 35°. Find the third angle.
44° · 35° · Missing triangle angles
3. Two interior angles of a triangle measure 83° and 73°. Find the third angle.
83° · 73° · Missing triangle angles
4. Two interior angles of a triangle measure 73° and 35°. Find the third angle.
73° · 35° · Missing triangle angles
5. Two interior angles of a triangle measure 53° and 46°. Find the third angle.
53° · 46° · Missing triangle angles
6. Two interior angles of a triangle measure 29° and 70°. Find the third angle.
29° · 70° · Missing triangle angles
7. Two interior angles of a triangle measure 78° and 61°. Find the third angle.
78° · 61° · Missing triangle angles
8. Two interior angles of a triangle measure 31° and 26°. Find the third angle.
31° · 26° · Missing triangle angles
9. Two interior angles of a triangle measure 30° and 28°. Find the third angle.
30° · 28° · Missing triangle angles
10. Two interior angles of a triangle measure 26° and 54°. Find the third angle.
26° · 54° · Missing triangle angles
11. Two interior angles of a triangle measure 51° and 27°. Find the third angle.
51° · 27° · Missing triangle angles
12. Two interior angles of a triangle measure 60° and 47°. Find the third angle.
60° · 47° · Missing triangle angles

12 questions · Seed 45 · 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 33° and 63°. Find the third angle.
84°
Angles in a triangle sum to 180°: 180° − (33° + 63°) = 84°.
2. Two interior angles of a triangle measure 44° and 35°. Find the third angle.
101°
Angles in a triangle sum to 180°: 180° − (44° + 35°) = 101°.
3. Two interior angles of a triangle measure 83° and 73°. Find the third angle.
24°
Angles in a triangle sum to 180°: 180° − (83° + 73°) = 24°.
4. Two interior angles of a triangle measure 73° and 35°. Find the third angle.
72°
Angles in a triangle sum to 180°: 180° − (73° + 35°) = 72°.
5. Two interior angles of a triangle measure 53° and 46°. Find the third angle.
81°
Angles in a triangle sum to 180°: 180° − (53° + 46°) = 81°.
6. Two interior angles of a triangle measure 29° and 70°. Find the third angle.
81°
Angles in a triangle sum to 180°: 180° − (29° + 70°) = 81°.
7. Two interior angles of a triangle measure 78° and 61°. Find the third angle.
41°
Angles in a triangle sum to 180°: 180° − (78° + 61°) = 41°.
8. Two interior angles of a triangle measure 31° and 26°. Find the third angle.
123°
Angles in a triangle sum to 180°: 180° − (31° + 26°) = 123°.
9. Two interior angles of a triangle measure 30° and 28°. Find the third angle.
122°
Angles in a triangle sum to 180°: 180° − (30° + 28°) = 122°.
10. Two interior angles of a triangle measure 26° and 54°. Find the third angle.
100°
Angles in a triangle sum to 180°: 180° − (26° + 54°) = 100°.
11. Two interior angles of a triangle measure 51° and 27°. Find the third angle.
102°
Angles in a triangle sum to 180°: 180° − (51° + 27°) = 102°.
12. Two interior angles of a triangle measure 60° and 47°. Find the third angle.
73°
Angles in a triangle sum to 180°: 180° − (60° + 47°) = 73°.

12 questions · Seed 45 · Age guidance, not curriculum certification