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 48° and 31°. Find the third angle.
48° · 31° · Missing triangle angles
2. Two interior angles of a triangle measure 35° and 42°. Find the third angle.
35° · 42° · Missing triangle angles
3. Two interior angles of a triangle measure 69° and 74°. Find the third angle.
69° · 74° · Missing triangle angles
4. Two interior angles of a triangle measure 38° and 56°. Find the third angle.
38° · 56° · Missing triangle angles
5. Two interior angles of a triangle measure 48° and 55°. Find the third angle.
48° · 55° · Missing triangle angles
6. Two interior angles of a triangle measure 78° and 51°. Find the third angle.
78° · 51° · Missing triangle angles
7. Two interior angles of a triangle measure 27° and 54°. Find the third angle.
27° · 54° · Missing triangle angles
8. Two interior angles of a triangle measure 43° and 28°. Find the third angle.
43° · 28° · Missing triangle angles
9. Two interior angles of a triangle measure 69° and 36°. Find the third angle.
69° · 36° · Missing triangle angles
10. Two interior angles of a triangle measure 61° and 66°. Find the third angle.
61° · 66° · Missing triangle angles
11. Two interior angles of a triangle measure 70° and 38°. Find the third angle.
70° · 38° · Missing triangle angles
12. Two interior angles of a triangle measure 70° and 32°. Find the third angle.
70° · 32° · Missing triangle angles

12 questions · Seed 104742 · 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 48° and 31°. Find the third angle.
101°
Angles in a triangle sum to 180°: 180° − (48° + 31°) = 101°.
2. Two interior angles of a triangle measure 35° and 42°. Find the third angle.
103°
Angles in a triangle sum to 180°: 180° − (35° + 42°) = 103°.
3. Two interior angles of a triangle measure 69° and 74°. Find the third angle.
37°
Angles in a triangle sum to 180°: 180° − (69° + 74°) = 37°.
4. Two interior angles of a triangle measure 38° and 56°. Find the third angle.
86°
Angles in a triangle sum to 180°: 180° − (38° + 56°) = 86°.
5. Two interior angles of a triangle measure 48° and 55°. Find the third angle.
77°
Angles in a triangle sum to 180°: 180° − (48° + 55°) = 77°.
6. Two interior angles of a triangle measure 78° and 51°. Find the third angle.
51°
Angles in a triangle sum to 180°: 180° − (78° + 51°) = 51°.
7. Two interior angles of a triangle measure 27° and 54°. Find the third angle.
99°
Angles in a triangle sum to 180°: 180° − (27° + 54°) = 99°.
8. Two interior angles of a triangle measure 43° and 28°. Find the third angle.
109°
Angles in a triangle sum to 180°: 180° − (43° + 28°) = 109°.
9. Two interior angles of a triangle measure 69° and 36°. Find the third angle.
75°
Angles in a triangle sum to 180°: 180° − (69° + 36°) = 75°.
10. Two interior angles of a triangle measure 61° and 66°. Find the third angle.
53°
Angles in a triangle sum to 180°: 180° − (61° + 66°) = 53°.
11. Two interior angles of a triangle measure 70° and 38°. Find the third angle.
72°
Angles in a triangle sum to 180°: 180° − (70° + 38°) = 72°.
12. Two interior angles of a triangle measure 70° and 32°. Find the third angle.
78°
Angles in a triangle sum to 180°: 180° − (70° + 32°) = 78°.

12 questions · Seed 104742 · 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 48° and 31°. Find the third angle.
48° · 31° · Missing triangle angles
2. Two interior angles of a triangle measure 35° and 42°. Find the third angle.
35° · 42° · Missing triangle angles
3. Two interior angles of a triangle measure 69° and 74°. Find the third angle.
69° · 74° · Missing triangle angles
4. Two interior angles of a triangle measure 38° and 56°. Find the third angle.
38° · 56° · Missing triangle angles
5. Two interior angles of a triangle measure 48° and 55°. Find the third angle.
48° · 55° · Missing triangle angles
6. Two interior angles of a triangle measure 78° and 51°. Find the third angle.
78° · 51° · Missing triangle angles
7. Two interior angles of a triangle measure 27° and 54°. Find the third angle.
27° · 54° · Missing triangle angles
8. Two interior angles of a triangle measure 43° and 28°. Find the third angle.
43° · 28° · Missing triangle angles
9. Two interior angles of a triangle measure 69° and 36°. Find the third angle.
69° · 36° · Missing triangle angles
10. Two interior angles of a triangle measure 61° and 66°. Find the third angle.
61° · 66° · Missing triangle angles
11. Two interior angles of a triangle measure 70° and 38°. Find the third angle.
70° · 38° · Missing triangle angles
12. Two interior angles of a triangle measure 70° and 32°. Find the third angle.
70° · 32° · Missing triangle angles

12 questions · Seed 104742 · 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 48° and 31°. Find the third angle.
101°
Angles in a triangle sum to 180°: 180° − (48° + 31°) = 101°.
2. Two interior angles of a triangle measure 35° and 42°. Find the third angle.
103°
Angles in a triangle sum to 180°: 180° − (35° + 42°) = 103°.
3. Two interior angles of a triangle measure 69° and 74°. Find the third angle.
37°
Angles in a triangle sum to 180°: 180° − (69° + 74°) = 37°.
4. Two interior angles of a triangle measure 38° and 56°. Find the third angle.
86°
Angles in a triangle sum to 180°: 180° − (38° + 56°) = 86°.
5. Two interior angles of a triangle measure 48° and 55°. Find the third angle.
77°
Angles in a triangle sum to 180°: 180° − (48° + 55°) = 77°.
6. Two interior angles of a triangle measure 78° and 51°. Find the third angle.
51°
Angles in a triangle sum to 180°: 180° − (78° + 51°) = 51°.
7. Two interior angles of a triangle measure 27° and 54°. Find the third angle.
99°
Angles in a triangle sum to 180°: 180° − (27° + 54°) = 99°.
8. Two interior angles of a triangle measure 43° and 28°. Find the third angle.
109°
Angles in a triangle sum to 180°: 180° − (43° + 28°) = 109°.
9. Two interior angles of a triangle measure 69° and 36°. Find the third angle.
75°
Angles in a triangle sum to 180°: 180° − (69° + 36°) = 75°.
10. Two interior angles of a triangle measure 61° and 66°. Find the third angle.
53°
Angles in a triangle sum to 180°: 180° − (61° + 66°) = 53°.
11. Two interior angles of a triangle measure 70° and 38°. Find the third angle.
72°
Angles in a triangle sum to 180°: 180° − (70° + 38°) = 72°.
12. Two interior angles of a triangle measure 70° and 32°. Find the third angle.
78°
Angles in a triangle sum to 180°: 180° − (70° + 32°) = 78°.

12 questions · Seed 104742 · Age guidance, not curriculum certification