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 40° and 67°. Find the third angle.
40° · 67° · Missing triangle angles
2. Two interior angles of a triangle measure 33° and 44°. Find the third angle.
33° · 44° · Missing triangle angles
3. Two interior angles of a triangle measure 52° and 74°. Find the third angle.
52° · 74° · Missing triangle angles
4. Two interior angles of a triangle measure 31° and 34°. Find the third angle.
31° · 34° · Missing triangle angles
5. Two interior angles of a triangle measure 49° and 32°. Find the third angle.
49° · 32° · Missing triangle angles
6. Two interior angles of a triangle measure 45° and 35°. Find the third angle.
45° · 35° · Missing triangle angles
7. Two interior angles of a triangle measure 69° and 59°. Find the third angle.
69° · 59° · Missing triangle angles
8. Two interior angles of a triangle measure 72° and 68°. Find the third angle.
72° · 68° · Missing triangle angles
9. Two interior angles of a triangle measure 28° and 69°. Find the third angle.
28° · 69° · Missing triangle angles
10. Two interior angles of a triangle measure 62° and 67°. Find the third angle.
62° · 67° · Missing triangle angles
11. Two interior angles of a triangle measure 79° and 61°. Find the third angle.
79° · 61° · Missing triangle angles
12. Two interior angles of a triangle measure 62° and 60°. Find the third angle.
62° · 60° · Missing triangle angles

12 questions · Seed 104738 · 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 40° and 67°. Find the third angle.
73°
Angles in a triangle sum to 180°: 180° − (40° + 67°) = 73°.
2. Two interior angles of a triangle measure 33° and 44°. Find the third angle.
103°
Angles in a triangle sum to 180°: 180° − (33° + 44°) = 103°.
3. Two interior angles of a triangle measure 52° and 74°. Find the third angle.
54°
Angles in a triangle sum to 180°: 180° − (52° + 74°) = 54°.
4. Two interior angles of a triangle measure 31° and 34°. Find the third angle.
115°
Angles in a triangle sum to 180°: 180° − (31° + 34°) = 115°.
5. Two interior angles of a triangle measure 49° and 32°. Find the third angle.
99°
Angles in a triangle sum to 180°: 180° − (49° + 32°) = 99°.
6. Two interior angles of a triangle measure 45° and 35°. Find the third angle.
100°
Angles in a triangle sum to 180°: 180° − (45° + 35°) = 100°.
7. Two interior angles of a triangle measure 69° and 59°. Find the third angle.
52°
Angles in a triangle sum to 180°: 180° − (69° + 59°) = 52°.
8. Two interior angles of a triangle measure 72° and 68°. Find the third angle.
40°
Angles in a triangle sum to 180°: 180° − (72° + 68°) = 40°.
9. Two interior angles of a triangle measure 28° and 69°. Find the third angle.
83°
Angles in a triangle sum to 180°: 180° − (28° + 69°) = 83°.
10. Two interior angles of a triangle measure 62° and 67°. Find the third angle.
51°
Angles in a triangle sum to 180°: 180° − (62° + 67°) = 51°.
11. Two interior angles of a triangle measure 79° and 61°. Find the third angle.
40°
Angles in a triangle sum to 180°: 180° − (79° + 61°) = 40°.
12. Two interior angles of a triangle measure 62° and 60°. Find the third angle.
58°
Angles in a triangle sum to 180°: 180° − (62° + 60°) = 58°.

12 questions · Seed 104738 · 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 40° and 67°. Find the third angle.
40° · 67° · Missing triangle angles
2. Two interior angles of a triangle measure 33° and 44°. Find the third angle.
33° · 44° · Missing triangle angles
3. Two interior angles of a triangle measure 52° and 74°. Find the third angle.
52° · 74° · Missing triangle angles
4. Two interior angles of a triangle measure 31° and 34°. Find the third angle.
31° · 34° · Missing triangle angles
5. Two interior angles of a triangle measure 49° and 32°. Find the third angle.
49° · 32° · Missing triangle angles
6. Two interior angles of a triangle measure 45° and 35°. Find the third angle.
45° · 35° · Missing triangle angles
7. Two interior angles of a triangle measure 69° and 59°. Find the third angle.
69° · 59° · Missing triangle angles
8. Two interior angles of a triangle measure 72° and 68°. Find the third angle.
72° · 68° · Missing triangle angles
9. Two interior angles of a triangle measure 28° and 69°. Find the third angle.
28° · 69° · Missing triangle angles
10. Two interior angles of a triangle measure 62° and 67°. Find the third angle.
62° · 67° · Missing triangle angles
11. Two interior angles of a triangle measure 79° and 61°. Find the third angle.
79° · 61° · Missing triangle angles
12. Two interior angles of a triangle measure 62° and 60°. Find the third angle.
62° · 60° · Missing triangle angles

12 questions · Seed 104738 · 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 40° and 67°. Find the third angle.
73°
Angles in a triangle sum to 180°: 180° − (40° + 67°) = 73°.
2. Two interior angles of a triangle measure 33° and 44°. Find the third angle.
103°
Angles in a triangle sum to 180°: 180° − (33° + 44°) = 103°.
3. Two interior angles of a triangle measure 52° and 74°. Find the third angle.
54°
Angles in a triangle sum to 180°: 180° − (52° + 74°) = 54°.
4. Two interior angles of a triangle measure 31° and 34°. Find the third angle.
115°
Angles in a triangle sum to 180°: 180° − (31° + 34°) = 115°.
5. Two interior angles of a triangle measure 49° and 32°. Find the third angle.
99°
Angles in a triangle sum to 180°: 180° − (49° + 32°) = 99°.
6. Two interior angles of a triangle measure 45° and 35°. Find the third angle.
100°
Angles in a triangle sum to 180°: 180° − (45° + 35°) = 100°.
7. Two interior angles of a triangle measure 69° and 59°. Find the third angle.
52°
Angles in a triangle sum to 180°: 180° − (69° + 59°) = 52°.
8. Two interior angles of a triangle measure 72° and 68°. Find the third angle.
40°
Angles in a triangle sum to 180°: 180° − (72° + 68°) = 40°.
9. Two interior angles of a triangle measure 28° and 69°. Find the third angle.
83°
Angles in a triangle sum to 180°: 180° − (28° + 69°) = 83°.
10. Two interior angles of a triangle measure 62° and 67°. Find the third angle.
51°
Angles in a triangle sum to 180°: 180° − (62° + 67°) = 51°.
11. Two interior angles of a triangle measure 79° and 61°. Find the third angle.
40°
Angles in a triangle sum to 180°: 180° − (79° + 61°) = 40°.
12. Two interior angles of a triangle measure 62° and 60°. Find the third angle.
58°
Angles in a triangle sum to 180°: 180° − (62° + 60°) = 58°.

12 questions · Seed 104738 · Age guidance, not curriculum certification