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 53° and 65°. Find the third angle.
53° · 65° · Missing triangle angles
2. Two interior angles of a triangle measure 67° and 50°. Find the third angle.
67° · 50° · Missing triangle angles
3. Two interior angles of a triangle measure 32° and 34°. Find the third angle.
32° · 34° · Missing triangle angles
4. Two interior angles of a triangle measure 33° and 56°. Find the third angle.
33° · 56° · Missing triangle angles
5. Two interior angles of a triangle measure 62° and 69°. Find the third angle.
62° · 69° · Missing triangle angles
6. Two interior angles of a triangle measure 43° and 32°. Find the third angle.
43° · 32° · Missing triangle angles
7. Two interior angles of a triangle measure 34° and 36°. Find the third angle.
34° · 36° · Missing triangle angles
8. Two interior angles of a triangle measure 83° and 64°. Find the third angle.
83° · 64° · Missing triangle angles
9. Two interior angles of a triangle measure 67° and 59°. Find the third angle.
67° · 59° · Missing triangle angles
10. Two interior angles of a triangle measure 80° and 72°. Find the third angle.
80° · 72° · Missing triangle angles
11. Two interior angles of a triangle measure 40° and 75°. Find the third angle.
40° · 75° · Missing triangle angles
12. Two interior angles of a triangle measure 33° and 53°. Find the third angle.
33° · 53° · Missing triangle angles

12 questions · Seed 104736 · 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 53° and 65°. Find the third angle.
62°
Angles in a triangle sum to 180°: 180° − (53° + 65°) = 62°.
2. Two interior angles of a triangle measure 67° and 50°. Find the third angle.
63°
Angles in a triangle sum to 180°: 180° − (67° + 50°) = 63°.
3. Two interior angles of a triangle measure 32° and 34°. Find the third angle.
114°
Angles in a triangle sum to 180°: 180° − (32° + 34°) = 114°.
4. Two interior angles of a triangle measure 33° and 56°. Find the third angle.
91°
Angles in a triangle sum to 180°: 180° − (33° + 56°) = 91°.
5. Two interior angles of a triangle measure 62° and 69°. Find the third angle.
49°
Angles in a triangle sum to 180°: 180° − (62° + 69°) = 49°.
6. Two interior angles of a triangle measure 43° and 32°. Find the third angle.
105°
Angles in a triangle sum to 180°: 180° − (43° + 32°) = 105°.
7. Two interior angles of a triangle measure 34° and 36°. Find the third angle.
110°
Angles in a triangle sum to 180°: 180° − (34° + 36°) = 110°.
8. Two interior angles of a triangle measure 83° and 64°. Find the third angle.
33°
Angles in a triangle sum to 180°: 180° − (83° + 64°) = 33°.
9. Two interior angles of a triangle measure 67° and 59°. Find the third angle.
54°
Angles in a triangle sum to 180°: 180° − (67° + 59°) = 54°.
10. Two interior angles of a triangle measure 80° and 72°. Find the third angle.
28°
Angles in a triangle sum to 180°: 180° − (80° + 72°) = 28°.
11. Two interior angles of a triangle measure 40° and 75°. Find the third angle.
65°
Angles in a triangle sum to 180°: 180° − (40° + 75°) = 65°.
12. Two interior angles of a triangle measure 33° and 53°. Find the third angle.
94°
Angles in a triangle sum to 180°: 180° − (33° + 53°) = 94°.

12 questions · Seed 104736 · 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 53° and 65°. Find the third angle.
53° · 65° · Missing triangle angles
2. Two interior angles of a triangle measure 67° and 50°. Find the third angle.
67° · 50° · Missing triangle angles
3. Two interior angles of a triangle measure 32° and 34°. Find the third angle.
32° · 34° · Missing triangle angles
4. Two interior angles of a triangle measure 33° and 56°. Find the third angle.
33° · 56° · Missing triangle angles
5. Two interior angles of a triangle measure 62° and 69°. Find the third angle.
62° · 69° · Missing triangle angles
6. Two interior angles of a triangle measure 43° and 32°. Find the third angle.
43° · 32° · Missing triangle angles
7. Two interior angles of a triangle measure 34° and 36°. Find the third angle.
34° · 36° · Missing triangle angles
8. Two interior angles of a triangle measure 83° and 64°. Find the third angle.
83° · 64° · Missing triangle angles
9. Two interior angles of a triangle measure 67° and 59°. Find the third angle.
67° · 59° · Missing triangle angles
10. Two interior angles of a triangle measure 80° and 72°. Find the third angle.
80° · 72° · Missing triangle angles
11. Two interior angles of a triangle measure 40° and 75°. Find the third angle.
40° · 75° · Missing triangle angles
12. Two interior angles of a triangle measure 33° and 53°. Find the third angle.
33° · 53° · Missing triangle angles

12 questions · Seed 104736 · 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 53° and 65°. Find the third angle.
62°
Angles in a triangle sum to 180°: 180° − (53° + 65°) = 62°.
2. Two interior angles of a triangle measure 67° and 50°. Find the third angle.
63°
Angles in a triangle sum to 180°: 180° − (67° + 50°) = 63°.
3. Two interior angles of a triangle measure 32° and 34°. Find the third angle.
114°
Angles in a triangle sum to 180°: 180° − (32° + 34°) = 114°.
4. Two interior angles of a triangle measure 33° and 56°. Find the third angle.
91°
Angles in a triangle sum to 180°: 180° − (33° + 56°) = 91°.
5. Two interior angles of a triangle measure 62° and 69°. Find the third angle.
49°
Angles in a triangle sum to 180°: 180° − (62° + 69°) = 49°.
6. Two interior angles of a triangle measure 43° and 32°. Find the third angle.
105°
Angles in a triangle sum to 180°: 180° − (43° + 32°) = 105°.
7. Two interior angles of a triangle measure 34° and 36°. Find the third angle.
110°
Angles in a triangle sum to 180°: 180° − (34° + 36°) = 110°.
8. Two interior angles of a triangle measure 83° and 64°. Find the third angle.
33°
Angles in a triangle sum to 180°: 180° − (83° + 64°) = 33°.
9. Two interior angles of a triangle measure 67° and 59°. Find the third angle.
54°
Angles in a triangle sum to 180°: 180° − (67° + 59°) = 54°.
10. Two interior angles of a triangle measure 80° and 72°. Find the third angle.
28°
Angles in a triangle sum to 180°: 180° − (80° + 72°) = 28°.
11. Two interior angles of a triangle measure 40° and 75°. Find the third angle.
65°
Angles in a triangle sum to 180°: 180° − (40° + 75°) = 65°.
12. Two interior angles of a triangle measure 33° and 53°. Find the third angle.
94°
Angles in a triangle sum to 180°: 180° − (33° + 53°) = 94°.

12 questions · Seed 104736 · Age guidance, not curriculum certification