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.

New variation Try interactive challenge Browse templates

Age band:Ages 10-12 Ages 13-15

Choose “Save as PDF” to keep a copy. Use your browser’s paper setting for A4 or Letter.

Worksheet StudioPractice pack · Ages 10-12

Missing triangle angles

Take your time. Show your thinking.

1. Two interior angles of a triangle measure 67° and 52°. Find the third angle.
67° · 52° · Missing triangle angles
2. Two interior angles of a triangle measure 82° and 25°. Find the third angle.
82° · 25° · Missing triangle angles
3. Two interior angles of a triangle measure 77° and 41°. Find the third angle.
77° · 41° · Missing triangle angles
4. Two interior angles of a triangle measure 81° and 45°. Find the third angle.
81° · 45° · Missing triangle angles
5. Two interior angles of a triangle measure 48° and 74°. Find the third angle.
48° · 74° · Missing triangle angles
6. Two interior angles of a triangle measure 57° and 75°. Find the third angle.
57° · 75° · Missing triangle angles
7. Two interior angles of a triangle measure 79° and 41°. Find the third angle.
79° · 41° · Missing triangle angles
8. Two interior angles of a triangle measure 69° and 54°. Find the third angle.
69° · 54° · Missing triangle angles
9. Two interior angles of a triangle measure 57° and 73°. Find the third angle.
57° · 73° · Missing triangle angles
10. Two interior angles of a triangle measure 61° and 41°. Find the third angle.
61° · 41° · Missing triangle angles
11. Two interior angles of a triangle measure 37° and 29°. Find the third angle.
37° · 29° · Missing triangle angles
12. Two interior angles of a triangle measure 26° and 55°. Find the third angle.
26° · 55° · Missing triangle angles

12 questions · Seed 104734 · 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 67° and 52°. Find the third angle.
61°
Angles in a triangle sum to 180°: 180° − (67° + 52°) = 61°.
2. Two interior angles of a triangle measure 82° and 25°. Find the third angle.
73°
Angles in a triangle sum to 180°: 180° − (82° + 25°) = 73°.
3. Two interior angles of a triangle measure 77° and 41°. Find the third angle.
62°
Angles in a triangle sum to 180°: 180° − (77° + 41°) = 62°.
4. Two interior angles of a triangle measure 81° and 45°. Find the third angle.
54°
Angles in a triangle sum to 180°: 180° − (81° + 45°) = 54°.
5. Two interior angles of a triangle measure 48° and 74°. Find the third angle.
58°
Angles in a triangle sum to 180°: 180° − (48° + 74°) = 58°.
6. Two interior angles of a triangle measure 57° and 75°. Find the third angle.
48°
Angles in a triangle sum to 180°: 180° − (57° + 75°) = 48°.
7. Two interior angles of a triangle measure 79° and 41°. Find the third angle.
60°
Angles in a triangle sum to 180°: 180° − (79° + 41°) = 60°.
8. Two interior angles of a triangle measure 69° and 54°. Find the third angle.
57°
Angles in a triangle sum to 180°: 180° − (69° + 54°) = 57°.
9. Two interior angles of a triangle measure 57° and 73°. Find the third angle.
50°
Angles in a triangle sum to 180°: 180° − (57° + 73°) = 50°.
10. Two interior angles of a triangle measure 61° and 41°. Find the third angle.
78°
Angles in a triangle sum to 180°: 180° − (61° + 41°) = 78°.
11. Two interior angles of a triangle measure 37° and 29°. Find the third angle.
114°
Angles in a triangle sum to 180°: 180° − (37° + 29°) = 114°.
12. Two interior angles of a triangle measure 26° and 55°. Find the third angle.
99°
Angles in a triangle sum to 180°: 180° − (26° + 55°) = 99°.

12 questions · Seed 104734 · 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 67° and 52°. Find the third angle.
67° · 52° · Missing triangle angles
2. Two interior angles of a triangle measure 82° and 25°. Find the third angle.
82° · 25° · Missing triangle angles
3. Two interior angles of a triangle measure 77° and 41°. Find the third angle.
77° · 41° · Missing triangle angles
4. Two interior angles of a triangle measure 81° and 45°. Find the third angle.
81° · 45° · Missing triangle angles
5. Two interior angles of a triangle measure 48° and 74°. Find the third angle.
48° · 74° · Missing triangle angles
6. Two interior angles of a triangle measure 57° and 75°. Find the third angle.
57° · 75° · Missing triangle angles
7. Two interior angles of a triangle measure 79° and 41°. Find the third angle.
79° · 41° · Missing triangle angles
8. Two interior angles of a triangle measure 69° and 54°. Find the third angle.
69° · 54° · Missing triangle angles
9. Two interior angles of a triangle measure 57° and 73°. Find the third angle.
57° · 73° · Missing triangle angles
10. Two interior angles of a triangle measure 61° and 41°. Find the third angle.
61° · 41° · Missing triangle angles
11. Two interior angles of a triangle measure 37° and 29°. Find the third angle.
37° · 29° · Missing triangle angles
12. Two interior angles of a triangle measure 26° and 55°. Find the third angle.
26° · 55° · Missing triangle angles

12 questions · Seed 104734 · 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 67° and 52°. Find the third angle.
61°
Angles in a triangle sum to 180°: 180° − (67° + 52°) = 61°.
2. Two interior angles of a triangle measure 82° and 25°. Find the third angle.
73°
Angles in a triangle sum to 180°: 180° − (82° + 25°) = 73°.
3. Two interior angles of a triangle measure 77° and 41°. Find the third angle.
62°
Angles in a triangle sum to 180°: 180° − (77° + 41°) = 62°.
4. Two interior angles of a triangle measure 81° and 45°. Find the third angle.
54°
Angles in a triangle sum to 180°: 180° − (81° + 45°) = 54°.
5. Two interior angles of a triangle measure 48° and 74°. Find the third angle.
58°
Angles in a triangle sum to 180°: 180° − (48° + 74°) = 58°.
6. Two interior angles of a triangle measure 57° and 75°. Find the third angle.
48°
Angles in a triangle sum to 180°: 180° − (57° + 75°) = 48°.
7. Two interior angles of a triangle measure 79° and 41°. Find the third angle.
60°
Angles in a triangle sum to 180°: 180° − (79° + 41°) = 60°.
8. Two interior angles of a triangle measure 69° and 54°. Find the third angle.
57°
Angles in a triangle sum to 180°: 180° − (69° + 54°) = 57°.
9. Two interior angles of a triangle measure 57° and 73°. Find the third angle.
50°
Angles in a triangle sum to 180°: 180° − (57° + 73°) = 50°.
10. Two interior angles of a triangle measure 61° and 41°. Find the third angle.
78°
Angles in a triangle sum to 180°: 180° − (61° + 41°) = 78°.
11. Two interior angles of a triangle measure 37° and 29°. Find the third angle.
114°
Angles in a triangle sum to 180°: 180° − (37° + 29°) = 114°.
12. Two interior angles of a triangle measure 26° and 55°. Find the third angle.
99°
Angles in a triangle sum to 180°: 180° − (26° + 55°) = 99°.

12 questions · Seed 104734 · Age guidance, not curriculum certification