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 50° and 43°. Find the third angle.
50° · 43° · Missing triangle angles
2. Two interior angles of a triangle measure 65° and 38°. Find the third angle.
65° · 38° · Missing triangle angles
3. Two interior angles of a triangle measure 47° and 62°. Find the third angle.
47° · 62° · Missing triangle angles
4. Two interior angles of a triangle measure 52° and 38°. Find the third angle.
52° · 38° · Missing triangle angles
5. Two interior angles of a triangle measure 34° and 30°. Find the third angle.
34° · 30° · Missing triangle angles
6. Two interior angles of a triangle measure 33° and 54°. Find the third angle.
33° · 54° · Missing triangle angles
7. Two interior angles of a triangle measure 44° and 25°. Find the third angle.
44° · 25° · Missing triangle angles
8. Two interior angles of a triangle measure 28° and 57°. Find the third angle.
28° · 57° · Missing triangle angles
9. Two interior angles of a triangle measure 36° and 39°. Find the third angle.
36° · 39° · Missing triangle angles
10. Two interior angles of a triangle measure 54° and 44°. Find the third angle.
54° · 44° · Missing triangle angles
11. Two interior angles of a triangle measure 54° and 28°. Find the third angle.
54° · 28° · Missing triangle angles
12. Two interior angles of a triangle measure 34° and 45°. Find the third angle.
34° · 45° · Missing triangle angles

12 questions · Seed 104744 · 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 50° and 43°. Find the third angle.
87°
Angles in a triangle sum to 180°: 180° − (50° + 43°) = 87°.
2. Two interior angles of a triangle measure 65° and 38°. Find the third angle.
77°
Angles in a triangle sum to 180°: 180° − (65° + 38°) = 77°.
3. Two interior angles of a triangle measure 47° and 62°. Find the third angle.
71°
Angles in a triangle sum to 180°: 180° − (47° + 62°) = 71°.
4. Two interior angles of a triangle measure 52° and 38°. Find the third angle.
90°
Angles in a triangle sum to 180°: 180° − (52° + 38°) = 90°.
5. Two interior angles of a triangle measure 34° and 30°. Find the third angle.
116°
Angles in a triangle sum to 180°: 180° − (34° + 30°) = 116°.
6. Two interior angles of a triangle measure 33° and 54°. Find the third angle.
93°
Angles in a triangle sum to 180°: 180° − (33° + 54°) = 93°.
7. Two interior angles of a triangle measure 44° and 25°. Find the third angle.
111°
Angles in a triangle sum to 180°: 180° − (44° + 25°) = 111°.
8. Two interior angles of a triangle measure 28° and 57°. Find the third angle.
95°
Angles in a triangle sum to 180°: 180° − (28° + 57°) = 95°.
9. Two interior angles of a triangle measure 36° and 39°. Find the third angle.
105°
Angles in a triangle sum to 180°: 180° − (36° + 39°) = 105°.
10. Two interior angles of a triangle measure 54° and 44°. Find the third angle.
82°
Angles in a triangle sum to 180°: 180° − (54° + 44°) = 82°.
11. Two interior angles of a triangle measure 54° and 28°. Find the third angle.
98°
Angles in a triangle sum to 180°: 180° − (54° + 28°) = 98°.
12. Two interior angles of a triangle measure 34° and 45°. Find the third angle.
101°
Angles in a triangle sum to 180°: 180° − (34° + 45°) = 101°.

12 questions · Seed 104744 · 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 50° and 43°. Find the third angle.
50° · 43° · Missing triangle angles
2. Two interior angles of a triangle measure 65° and 38°. Find the third angle.
65° · 38° · Missing triangle angles
3. Two interior angles of a triangle measure 47° and 62°. Find the third angle.
47° · 62° · Missing triangle angles
4. Two interior angles of a triangle measure 52° and 38°. Find the third angle.
52° · 38° · Missing triangle angles
5. Two interior angles of a triangle measure 34° and 30°. Find the third angle.
34° · 30° · Missing triangle angles
6. Two interior angles of a triangle measure 33° and 54°. Find the third angle.
33° · 54° · Missing triangle angles
7. Two interior angles of a triangle measure 44° and 25°. Find the third angle.
44° · 25° · Missing triangle angles
8. Two interior angles of a triangle measure 28° and 57°. Find the third angle.
28° · 57° · Missing triangle angles
9. Two interior angles of a triangle measure 36° and 39°. Find the third angle.
36° · 39° · Missing triangle angles
10. Two interior angles of a triangle measure 54° and 44°. Find the third angle.
54° · 44° · Missing triangle angles
11. Two interior angles of a triangle measure 54° and 28°. Find the third angle.
54° · 28° · Missing triangle angles
12. Two interior angles of a triangle measure 34° and 45°. Find the third angle.
34° · 45° · Missing triangle angles

12 questions · Seed 104744 · 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 50° and 43°. Find the third angle.
87°
Angles in a triangle sum to 180°: 180° − (50° + 43°) = 87°.
2. Two interior angles of a triangle measure 65° and 38°. Find the third angle.
77°
Angles in a triangle sum to 180°: 180° − (65° + 38°) = 77°.
3. Two interior angles of a triangle measure 47° and 62°. Find the third angle.
71°
Angles in a triangle sum to 180°: 180° − (47° + 62°) = 71°.
4. Two interior angles of a triangle measure 52° and 38°. Find the third angle.
90°
Angles in a triangle sum to 180°: 180° − (52° + 38°) = 90°.
5. Two interior angles of a triangle measure 34° and 30°. Find the third angle.
116°
Angles in a triangle sum to 180°: 180° − (34° + 30°) = 116°.
6. Two interior angles of a triangle measure 33° and 54°. Find the third angle.
93°
Angles in a triangle sum to 180°: 180° − (33° + 54°) = 93°.
7. Two interior angles of a triangle measure 44° and 25°. Find the third angle.
111°
Angles in a triangle sum to 180°: 180° − (44° + 25°) = 111°.
8. Two interior angles of a triangle measure 28° and 57°. Find the third angle.
95°
Angles in a triangle sum to 180°: 180° − (28° + 57°) = 95°.
9. Two interior angles of a triangle measure 36° and 39°. Find the third angle.
105°
Angles in a triangle sum to 180°: 180° − (36° + 39°) = 105°.
10. Two interior angles of a triangle measure 54° and 44°. Find the third angle.
82°
Angles in a triangle sum to 180°: 180° − (54° + 44°) = 82°.
11. Two interior angles of a triangle measure 54° and 28°. Find the third angle.
98°
Angles in a triangle sum to 180°: 180° − (54° + 28°) = 98°.
12. Two interior angles of a triangle measure 34° and 45°. Find the third angle.
101°
Angles in a triangle sum to 180°: 180° − (34° + 45°) = 101°.

12 questions · Seed 104744 · Age guidance, not curriculum certification