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 51° and 36°. Find the third angle.
51° · 36° · Missing triangle angles
2. Two interior angles of a triangle measure 43° and 32°. Find the third angle.
43° · 32° · Missing triangle angles
3. Two interior angles of a triangle measure 82° and 42°. Find the third angle.
82° · 42° · Missing triangle angles
4. Two interior angles of a triangle measure 60° and 34°. Find the third angle.
60° · 34° · Missing triangle angles
5. Two interior angles of a triangle measure 44° and 54°. Find the third angle.
44° · 54° · 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 50° and 73°. Find the third angle.
50° · 73° · Missing triangle angles
8. Two interior angles of a triangle measure 47° and 66°. Find the third angle.
47° · 66° · Missing triangle angles
9. Two interior angles of a triangle measure 71° and 42°. Find the third angle.
71° · 42° · Missing triangle angles
10. Two interior angles of a triangle measure 68° and 59°. Find the third angle.
68° · 59° · Missing triangle angles
11. Two interior angles of a triangle measure 47° and 69°. Find the third angle.
47° · 69° · Missing triangle angles
12. Two interior angles of a triangle measure 49° and 65°. Find the third angle.
49° · 65° · Missing triangle angles

12 questions · Seed 55 · 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 51° and 36°. Find the third angle.
93°
Angles in a triangle sum to 180°: 180° − (51° + 36°) = 93°.
2. Two interior angles of a triangle measure 43° and 32°. Find the third angle.
105°
Angles in a triangle sum to 180°: 180° − (43° + 32°) = 105°.
3. Two interior angles of a triangle measure 82° and 42°. Find the third angle.
56°
Angles in a triangle sum to 180°: 180° − (82° + 42°) = 56°.
4. Two interior angles of a triangle measure 60° and 34°. Find the third angle.
86°
Angles in a triangle sum to 180°: 180° − (60° + 34°) = 86°.
5. Two interior angles of a triangle measure 44° and 54°. Find the third angle.
82°
Angles in a triangle sum to 180°: 180° − (44° + 54°) = 82°.
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 50° and 73°. Find the third angle.
57°
Angles in a triangle sum to 180°: 180° − (50° + 73°) = 57°.
8. Two interior angles of a triangle measure 47° and 66°. Find the third angle.
67°
Angles in a triangle sum to 180°: 180° − (47° + 66°) = 67°.
9. Two interior angles of a triangle measure 71° and 42°. Find the third angle.
67°
Angles in a triangle sum to 180°: 180° − (71° + 42°) = 67°.
10. Two interior angles of a triangle measure 68° and 59°. Find the third angle.
53°
Angles in a triangle sum to 180°: 180° − (68° + 59°) = 53°.
11. Two interior angles of a triangle measure 47° and 69°. Find the third angle.
64°
Angles in a triangle sum to 180°: 180° − (47° + 69°) = 64°.
12. Two interior angles of a triangle measure 49° and 65°. Find the third angle.
66°
Angles in a triangle sum to 180°: 180° − (49° + 65°) = 66°.

12 questions · Seed 55 · 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 51° and 36°. Find the third angle.
51° · 36° · Missing triangle angles
2. Two interior angles of a triangle measure 43° and 32°. Find the third angle.
43° · 32° · Missing triangle angles
3. Two interior angles of a triangle measure 82° and 42°. Find the third angle.
82° · 42° · Missing triangle angles
4. Two interior angles of a triangle measure 60° and 34°. Find the third angle.
60° · 34° · Missing triangle angles
5. Two interior angles of a triangle measure 44° and 54°. Find the third angle.
44° · 54° · 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 50° and 73°. Find the third angle.
50° · 73° · Missing triangle angles
8. Two interior angles of a triangle measure 47° and 66°. Find the third angle.
47° · 66° · Missing triangle angles
9. Two interior angles of a triangle measure 71° and 42°. Find the third angle.
71° · 42° · Missing triangle angles
10. Two interior angles of a triangle measure 68° and 59°. Find the third angle.
68° · 59° · Missing triangle angles
11. Two interior angles of a triangle measure 47° and 69°. Find the third angle.
47° · 69° · Missing triangle angles
12. Two interior angles of a triangle measure 49° and 65°. Find the third angle.
49° · 65° · Missing triangle angles

12 questions · Seed 55 · 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 51° and 36°. Find the third angle.
93°
Angles in a triangle sum to 180°: 180° − (51° + 36°) = 93°.
2. Two interior angles of a triangle measure 43° and 32°. Find the third angle.
105°
Angles in a triangle sum to 180°: 180° − (43° + 32°) = 105°.
3. Two interior angles of a triangle measure 82° and 42°. Find the third angle.
56°
Angles in a triangle sum to 180°: 180° − (82° + 42°) = 56°.
4. Two interior angles of a triangle measure 60° and 34°. Find the third angle.
86°
Angles in a triangle sum to 180°: 180° − (60° + 34°) = 86°.
5. Two interior angles of a triangle measure 44° and 54°. Find the third angle.
82°
Angles in a triangle sum to 180°: 180° − (44° + 54°) = 82°.
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 50° and 73°. Find the third angle.
57°
Angles in a triangle sum to 180°: 180° − (50° + 73°) = 57°.
8. Two interior angles of a triangle measure 47° and 66°. Find the third angle.
67°
Angles in a triangle sum to 180°: 180° − (47° + 66°) = 67°.
9. Two interior angles of a triangle measure 71° and 42°. Find the third angle.
67°
Angles in a triangle sum to 180°: 180° − (71° + 42°) = 67°.
10. Two interior angles of a triangle measure 68° and 59°. Find the third angle.
53°
Angles in a triangle sum to 180°: 180° − (68° + 59°) = 53°.
11. Two interior angles of a triangle measure 47° and 69°. Find the third angle.
64°
Angles in a triangle sum to 180°: 180° − (47° + 69°) = 64°.
12. Two interior angles of a triangle measure 49° and 65°. Find the third angle.
66°
Angles in a triangle sum to 180°: 180° − (49° + 65°) = 66°.

12 questions · Seed 55 · Age guidance, not curriculum certification