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 46° and 75°. Find the third angle.
46° · 75° · Missing triangle angles
2. Two interior angles of a triangle measure 60° and 74°. Find the third angle.
60° · 74° · Missing triangle angles
3. Two interior angles of a triangle measure 82° and 44°. Find the third angle.
82° · 44° · Missing triangle angles
4. Two interior angles of a triangle measure 26° and 66°. Find the third angle.
26° · 66° · Missing triangle angles
5. Two interior angles of a triangle measure 31° and 39°. Find the third angle.
31° · 39° · Missing triangle angles
6. Two interior angles of a triangle measure 32° and 47°. Find the third angle.
32° · 47° · Missing triangle angles
7. Two interior angles of a triangle measure 54° and 69°. Find the third angle.
54° · 69° · Missing triangle angles
8. Two interior angles of a triangle measure 34° and 41°. Find the third angle.
34° · 41° · Missing triangle angles
9. Two interior angles of a triangle measure 58° and 61°. Find the third angle.
58° · 61° · Missing triangle angles
10. Two interior angles of a triangle measure 77° and 39°. Find the third angle.
77° · 39° · Missing triangle angles
11. Two interior angles of a triangle measure 52° and 29°. Find the third angle.
52° · 29° · Missing triangle angles
12. Two interior angles of a triangle measure 68° and 54°. Find the third angle.
68° · 54° · Missing triangle angles

12 questions · Seed 44 · 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 46° and 75°. Find the third angle.
59°
Angles in a triangle sum to 180°: 180° − (46° + 75°) = 59°.
2. Two interior angles of a triangle measure 60° and 74°. Find the third angle.
46°
Angles in a triangle sum to 180°: 180° − (60° + 74°) = 46°.
3. Two interior angles of a triangle measure 82° and 44°. Find the third angle.
54°
Angles in a triangle sum to 180°: 180° − (82° + 44°) = 54°.
4. Two interior angles of a triangle measure 26° and 66°. Find the third angle.
88°
Angles in a triangle sum to 180°: 180° − (26° + 66°) = 88°.
5. Two interior angles of a triangle measure 31° and 39°. Find the third angle.
110°
Angles in a triangle sum to 180°: 180° − (31° + 39°) = 110°.
6. Two interior angles of a triangle measure 32° and 47°. Find the third angle.
101°
Angles in a triangle sum to 180°: 180° − (32° + 47°) = 101°.
7. Two interior angles of a triangle measure 54° and 69°. Find the third angle.
57°
Angles in a triangle sum to 180°: 180° − (54° + 69°) = 57°.
8. Two interior angles of a triangle measure 34° and 41°. Find the third angle.
105°
Angles in a triangle sum to 180°: 180° − (34° + 41°) = 105°.
9. Two interior angles of a triangle measure 58° and 61°. Find the third angle.
61°
Angles in a triangle sum to 180°: 180° − (58° + 61°) = 61°.
10. Two interior angles of a triangle measure 77° and 39°. Find the third angle.
64°
Angles in a triangle sum to 180°: 180° − (77° + 39°) = 64°.
11. Two interior angles of a triangle measure 52° and 29°. Find the third angle.
99°
Angles in a triangle sum to 180°: 180° − (52° + 29°) = 99°.
12. Two interior angles of a triangle measure 68° and 54°. Find the third angle.
58°
Angles in a triangle sum to 180°: 180° − (68° + 54°) = 58°.

12 questions · Seed 44 · 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 46° and 75°. Find the third angle.
46° · 75° · Missing triangle angles
2. Two interior angles of a triangle measure 60° and 74°. Find the third angle.
60° · 74° · Missing triangle angles
3. Two interior angles of a triangle measure 82° and 44°. Find the third angle.
82° · 44° · Missing triangle angles
4. Two interior angles of a triangle measure 26° and 66°. Find the third angle.
26° · 66° · Missing triangle angles
5. Two interior angles of a triangle measure 31° and 39°. Find the third angle.
31° · 39° · Missing triangle angles
6. Two interior angles of a triangle measure 32° and 47°. Find the third angle.
32° · 47° · Missing triangle angles
7. Two interior angles of a triangle measure 54° and 69°. Find the third angle.
54° · 69° · Missing triangle angles
8. Two interior angles of a triangle measure 34° and 41°. Find the third angle.
34° · 41° · Missing triangle angles
9. Two interior angles of a triangle measure 58° and 61°. Find the third angle.
58° · 61° · Missing triangle angles
10. Two interior angles of a triangle measure 77° and 39°. Find the third angle.
77° · 39° · Missing triangle angles
11. Two interior angles of a triangle measure 52° and 29°. Find the third angle.
52° · 29° · Missing triangle angles
12. Two interior angles of a triangle measure 68° and 54°. Find the third angle.
68° · 54° · Missing triangle angles

12 questions · Seed 44 · 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 46° and 75°. Find the third angle.
59°
Angles in a triangle sum to 180°: 180° − (46° + 75°) = 59°.
2. Two interior angles of a triangle measure 60° and 74°. Find the third angle.
46°
Angles in a triangle sum to 180°: 180° − (60° + 74°) = 46°.
3. Two interior angles of a triangle measure 82° and 44°. Find the third angle.
54°
Angles in a triangle sum to 180°: 180° − (82° + 44°) = 54°.
4. Two interior angles of a triangle measure 26° and 66°. Find the third angle.
88°
Angles in a triangle sum to 180°: 180° − (26° + 66°) = 88°.
5. Two interior angles of a triangle measure 31° and 39°. Find the third angle.
110°
Angles in a triangle sum to 180°: 180° − (31° + 39°) = 110°.
6. Two interior angles of a triangle measure 32° and 47°. Find the third angle.
101°
Angles in a triangle sum to 180°: 180° − (32° + 47°) = 101°.
7. Two interior angles of a triangle measure 54° and 69°. Find the third angle.
57°
Angles in a triangle sum to 180°: 180° − (54° + 69°) = 57°.
8. Two interior angles of a triangle measure 34° and 41°. Find the third angle.
105°
Angles in a triangle sum to 180°: 180° − (34° + 41°) = 105°.
9. Two interior angles of a triangle measure 58° and 61°. Find the third angle.
61°
Angles in a triangle sum to 180°: 180° − (58° + 61°) = 61°.
10. Two interior angles of a triangle measure 77° and 39°. Find the third angle.
64°
Angles in a triangle sum to 180°: 180° − (77° + 39°) = 64°.
11. Two interior angles of a triangle measure 52° and 29°. Find the third angle.
99°
Angles in a triangle sum to 180°: 180° − (52° + 29°) = 99°.
12. Two interior angles of a triangle measure 68° and 54°. Find the third angle.
58°
Angles in a triangle sum to 180°: 180° − (68° + 54°) = 58°.

12 questions · Seed 44 · Age guidance, not curriculum certification