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 68° and 75°. Find the third angle.
68° · 75° · Missing triangle angles
2. Two interior angles of a triangle measure 57° and 42°. Find the third angle.
57° · 42° · Missing triangle angles
3. Two interior angles of a triangle measure 47° and 41°. Find the third angle.
47° · 41° · Missing triangle angles
4. Two interior angles of a triangle measure 78° and 38°. Find the third angle.
78° · 38° · Missing triangle angles
5. Two interior angles of a triangle measure 79° and 75°. Find the third angle.
79° · 75° · Missing triangle angles
6. Two interior angles of a triangle measure 58° and 34°. Find the third angle.
58° · 34° · Missing triangle angles
7. Two interior angles of a triangle measure 47° and 74°. Find the third angle.
47° · 74° · Missing triangle angles
8. Two interior angles of a triangle measure 63° and 65°. Find the third angle.
63° · 65° · Missing triangle angles
9. Two interior angles of a triangle measure 34° and 42°. Find the third angle.
34° · 42° · Missing triangle angles
10. Two interior angles of a triangle measure 52° and 55°. Find the third angle.
52° · 55° · Missing triangle angles
11. Two interior angles of a triangle measure 45° and 37°. Find the third angle.
45° · 37° · Missing triangle angles
12. Two interior angles of a triangle measure 33° and 38°. Find the third angle.
33° · 38° · Missing triangle angles

12 questions · Seed 53 · 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 68° and 75°. Find the third angle.
37°
Angles in a triangle sum to 180°: 180° − (68° + 75°) = 37°.
2. Two interior angles of a triangle measure 57° and 42°. Find the third angle.
81°
Angles in a triangle sum to 180°: 180° − (57° + 42°) = 81°.
3. Two interior angles of a triangle measure 47° and 41°. Find the third angle.
92°
Angles in a triangle sum to 180°: 180° − (47° + 41°) = 92°.
4. Two interior angles of a triangle measure 78° and 38°. Find the third angle.
64°
Angles in a triangle sum to 180°: 180° − (78° + 38°) = 64°.
5. Two interior angles of a triangle measure 79° and 75°. Find the third angle.
26°
Angles in a triangle sum to 180°: 180° − (79° + 75°) = 26°.
6. Two interior angles of a triangle measure 58° and 34°. Find the third angle.
88°
Angles in a triangle sum to 180°: 180° − (58° + 34°) = 88°.
7. Two interior angles of a triangle measure 47° and 74°. Find the third angle.
59°
Angles in a triangle sum to 180°: 180° − (47° + 74°) = 59°.
8. Two interior angles of a triangle measure 63° and 65°. Find the third angle.
52°
Angles in a triangle sum to 180°: 180° − (63° + 65°) = 52°.
9. Two interior angles of a triangle measure 34° and 42°. Find the third angle.
104°
Angles in a triangle sum to 180°: 180° − (34° + 42°) = 104°.
10. Two interior angles of a triangle measure 52° and 55°. Find the third angle.
73°
Angles in a triangle sum to 180°: 180° − (52° + 55°) = 73°.
11. Two interior angles of a triangle measure 45° and 37°. Find the third angle.
98°
Angles in a triangle sum to 180°: 180° − (45° + 37°) = 98°.
12. Two interior angles of a triangle measure 33° and 38°. Find the third angle.
109°
Angles in a triangle sum to 180°: 180° − (33° + 38°) = 109°.

12 questions · Seed 53 · 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 68° and 75°. Find the third angle.
68° · 75° · Missing triangle angles
2. Two interior angles of a triangle measure 57° and 42°. Find the third angle.
57° · 42° · Missing triangle angles
3. Two interior angles of a triangle measure 47° and 41°. Find the third angle.
47° · 41° · Missing triangle angles
4. Two interior angles of a triangle measure 78° and 38°. Find the third angle.
78° · 38° · Missing triangle angles
5. Two interior angles of a triangle measure 79° and 75°. Find the third angle.
79° · 75° · Missing triangle angles
6. Two interior angles of a triangle measure 58° and 34°. Find the third angle.
58° · 34° · Missing triangle angles
7. Two interior angles of a triangle measure 47° and 74°. Find the third angle.
47° · 74° · Missing triangle angles
8. Two interior angles of a triangle measure 63° and 65°. Find the third angle.
63° · 65° · Missing triangle angles
9. Two interior angles of a triangle measure 34° and 42°. Find the third angle.
34° · 42° · Missing triangle angles
10. Two interior angles of a triangle measure 52° and 55°. Find the third angle.
52° · 55° · Missing triangle angles
11. Two interior angles of a triangle measure 45° and 37°. Find the third angle.
45° · 37° · Missing triangle angles
12. Two interior angles of a triangle measure 33° and 38°. Find the third angle.
33° · 38° · Missing triangle angles

12 questions · Seed 53 · 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 68° and 75°. Find the third angle.
37°
Angles in a triangle sum to 180°: 180° − (68° + 75°) = 37°.
2. Two interior angles of a triangle measure 57° and 42°. Find the third angle.
81°
Angles in a triangle sum to 180°: 180° − (57° + 42°) = 81°.
3. Two interior angles of a triangle measure 47° and 41°. Find the third angle.
92°
Angles in a triangle sum to 180°: 180° − (47° + 41°) = 92°.
4. Two interior angles of a triangle measure 78° and 38°. Find the third angle.
64°
Angles in a triangle sum to 180°: 180° − (78° + 38°) = 64°.
5. Two interior angles of a triangle measure 79° and 75°. Find the third angle.
26°
Angles in a triangle sum to 180°: 180° − (79° + 75°) = 26°.
6. Two interior angles of a triangle measure 58° and 34°. Find the third angle.
88°
Angles in a triangle sum to 180°: 180° − (58° + 34°) = 88°.
7. Two interior angles of a triangle measure 47° and 74°. Find the third angle.
59°
Angles in a triangle sum to 180°: 180° − (47° + 74°) = 59°.
8. Two interior angles of a triangle measure 63° and 65°. Find the third angle.
52°
Angles in a triangle sum to 180°: 180° − (63° + 65°) = 52°.
9. Two interior angles of a triangle measure 34° and 42°. Find the third angle.
104°
Angles in a triangle sum to 180°: 180° − (34° + 42°) = 104°.
10. Two interior angles of a triangle measure 52° and 55°. Find the third angle.
73°
Angles in a triangle sum to 180°: 180° − (52° + 55°) = 73°.
11. Two interior angles of a triangle measure 45° and 37°. Find the third angle.
98°
Angles in a triangle sum to 180°: 180° − (45° + 37°) = 98°.
12. Two interior angles of a triangle measure 33° and 38°. Find the third angle.
109°
Angles in a triangle sum to 180°: 180° − (33° + 38°) = 109°.

12 questions · Seed 53 · Age guidance, not curriculum certification