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 72°. Find the third angle.
61° · 72° · Missing triangle angles
2. Two interior angles of a triangle measure 74° and 67°. Find the third angle.
74° · 67° · Missing triangle angles
3. Two interior angles of a triangle measure 73° and 52°. Find the third angle.
73° · 52° · Missing triangle angles
4. Two interior angles of a triangle measure 81° and 68°. Find the third angle.
81° · 68° · Missing triangle angles
5. Two interior angles of a triangle measure 57° and 69°. Find the third angle.
57° · 69° · Missing triangle angles
6. Two interior angles of a triangle measure 81° and 69°. Find the third angle.
81° · 69° · Missing triangle angles
7. Two interior angles of a triangle measure 33° and 43°. Find the third angle.
33° · 43° · Missing triangle angles
8. Two interior angles of a triangle measure 32° and 68°. Find the third angle.
32° · 68° · Missing triangle angles
9. Two interior angles of a triangle measure 25° and 35°. Find the third angle.
25° · 35° · Missing triangle angles
10. Two interior angles of a triangle measure 42° and 31°. Find the third angle.
42° · 31° · Missing triangle angles
11. Two interior angles of a triangle measure 36° and 54°. Find the third angle.
36° · 54° · Missing triangle angles
12. Two interior angles of a triangle measure 79° and 40°. Find the third angle.
79° · 40° · Missing triangle angles

12 questions · Seed 104730 · 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 72°. Find the third angle.
47°
Angles in a triangle sum to 180°: 180° − (61° + 72°) = 47°.
2. Two interior angles of a triangle measure 74° and 67°. Find the third angle.
39°
Angles in a triangle sum to 180°: 180° − (74° + 67°) = 39°.
3. Two interior angles of a triangle measure 73° and 52°. Find the third angle.
55°
Angles in a triangle sum to 180°: 180° − (73° + 52°) = 55°.
4. Two interior angles of a triangle measure 81° and 68°. Find the third angle.
31°
Angles in a triangle sum to 180°: 180° − (81° + 68°) = 31°.
5. Two interior angles of a triangle measure 57° and 69°. Find the third angle.
54°
Angles in a triangle sum to 180°: 180° − (57° + 69°) = 54°.
6. Two interior angles of a triangle measure 81° and 69°. Find the third angle.
30°
Angles in a triangle sum to 180°: 180° − (81° + 69°) = 30°.
7. Two interior angles of a triangle measure 33° and 43°. Find the third angle.
104°
Angles in a triangle sum to 180°: 180° − (33° + 43°) = 104°.
8. Two interior angles of a triangle measure 32° and 68°. Find the third angle.
80°
Angles in a triangle sum to 180°: 180° − (32° + 68°) = 80°.
9. Two interior angles of a triangle measure 25° and 35°. Find the third angle.
120°
Angles in a triangle sum to 180°: 180° − (25° + 35°) = 120°.
10. Two interior angles of a triangle measure 42° and 31°. Find the third angle.
107°
Angles in a triangle sum to 180°: 180° − (42° + 31°) = 107°.
11. Two interior angles of a triangle measure 36° and 54°. Find the third angle.
90°
Angles in a triangle sum to 180°: 180° − (36° + 54°) = 90°.
12. Two interior angles of a triangle measure 79° and 40°. Find the third angle.
61°
Angles in a triangle sum to 180°: 180° − (79° + 40°) = 61°.

12 questions · Seed 104730 · 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 72°. Find the third angle.
61° · 72° · Missing triangle angles
2. Two interior angles of a triangle measure 74° and 67°. Find the third angle.
74° · 67° · Missing triangle angles
3. Two interior angles of a triangle measure 73° and 52°. Find the third angle.
73° · 52° · Missing triangle angles
4. Two interior angles of a triangle measure 81° and 68°. Find the third angle.
81° · 68° · Missing triangle angles
5. Two interior angles of a triangle measure 57° and 69°. Find the third angle.
57° · 69° · Missing triangle angles
6. Two interior angles of a triangle measure 81° and 69°. Find the third angle.
81° · 69° · Missing triangle angles
7. Two interior angles of a triangle measure 33° and 43°. Find the third angle.
33° · 43° · Missing triangle angles
8. Two interior angles of a triangle measure 32° and 68°. Find the third angle.
32° · 68° · Missing triangle angles
9. Two interior angles of a triangle measure 25° and 35°. Find the third angle.
25° · 35° · Missing triangle angles
10. Two interior angles of a triangle measure 42° and 31°. Find the third angle.
42° · 31° · Missing triangle angles
11. Two interior angles of a triangle measure 36° and 54°. Find the third angle.
36° · 54° · Missing triangle angles
12. Two interior angles of a triangle measure 79° and 40°. Find the third angle.
79° · 40° · Missing triangle angles

12 questions · Seed 104730 · 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 72°. Find the third angle.
47°
Angles in a triangle sum to 180°: 180° − (61° + 72°) = 47°.
2. Two interior angles of a triangle measure 74° and 67°. Find the third angle.
39°
Angles in a triangle sum to 180°: 180° − (74° + 67°) = 39°.
3. Two interior angles of a triangle measure 73° and 52°. Find the third angle.
55°
Angles in a triangle sum to 180°: 180° − (73° + 52°) = 55°.
4. Two interior angles of a triangle measure 81° and 68°. Find the third angle.
31°
Angles in a triangle sum to 180°: 180° − (81° + 68°) = 31°.
5. Two interior angles of a triangle measure 57° and 69°. Find the third angle.
54°
Angles in a triangle sum to 180°: 180° − (57° + 69°) = 54°.
6. Two interior angles of a triangle measure 81° and 69°. Find the third angle.
30°
Angles in a triangle sum to 180°: 180° − (81° + 69°) = 30°.
7. Two interior angles of a triangle measure 33° and 43°. Find the third angle.
104°
Angles in a triangle sum to 180°: 180° − (33° + 43°) = 104°.
8. Two interior angles of a triangle measure 32° and 68°. Find the third angle.
80°
Angles in a triangle sum to 180°: 180° − (32° + 68°) = 80°.
9. Two interior angles of a triangle measure 25° and 35°. Find the third angle.
120°
Angles in a triangle sum to 180°: 180° − (25° + 35°) = 120°.
10. Two interior angles of a triangle measure 42° and 31°. Find the third angle.
107°
Angles in a triangle sum to 180°: 180° − (42° + 31°) = 107°.
11. Two interior angles of a triangle measure 36° and 54°. Find the third angle.
90°
Angles in a triangle sum to 180°: 180° − (36° + 54°) = 90°.
12. Two interior angles of a triangle measure 79° and 40°. Find the third angle.
61°
Angles in a triangle sum to 180°: 180° − (79° + 40°) = 61°.

12 questions · Seed 104730 · Age guidance, not curriculum certification