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 59° and 56°. Find the third angle.
59° · 56° · Missing triangle angles
2. Two interior angles of a triangle measure 48° and 36°. Find the third angle.
48° · 36° · Missing triangle angles
3. Two interior angles of a triangle measure 68° and 59°. Find the third angle.
68° · 59° · Missing triangle angles
4. Two interior angles of a triangle measure 58° and 26°. Find the third angle.
58° · 26° · Missing triangle angles
5. Two interior angles of a triangle measure 59° and 57°. Find the third angle.
59° · 57° · Missing triangle angles
6. Two interior angles of a triangle measure 81° and 65°. Find the third angle.
81° · 65° · Missing triangle angles
7. Two interior angles of a triangle measure 46° and 73°. Find the third angle.
46° · 73° · Missing triangle angles
8. Two interior angles of a triangle measure 70° and 30°. Find the third angle.
70° · 30° · Missing triangle angles
9. Two interior angles of a triangle measure 45° and 52°. Find the third angle.
45° · 52° · Missing triangle angles
10. Two interior angles of a triangle measure 34° and 31°. Find the third angle.
34° · 31° · Missing triangle angles
11. Two interior angles of a triangle measure 35° and 49°. Find the third angle.
35° · 49° · Missing triangle angles
12. Two interior angles of a triangle measure 82° and 68°. Find the third angle.
82° · 68° · Missing triangle angles

12 questions · Seed 67 · 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 59° and 56°. Find the third angle.
65°
Angles in a triangle sum to 180°: 180° − (59° + 56°) = 65°.
2. Two interior angles of a triangle measure 48° and 36°. Find the third angle.
96°
Angles in a triangle sum to 180°: 180° − (48° + 36°) = 96°.
3. 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°.
4. Two interior angles of a triangle measure 58° and 26°. Find the third angle.
96°
Angles in a triangle sum to 180°: 180° − (58° + 26°) = 96°.
5. Two interior angles of a triangle measure 59° and 57°. Find the third angle.
64°
Angles in a triangle sum to 180°: 180° − (59° + 57°) = 64°.
6. Two interior angles of a triangle measure 81° and 65°. Find the third angle.
34°
Angles in a triangle sum to 180°: 180° − (81° + 65°) = 34°.
7. Two interior angles of a triangle measure 46° and 73°. Find the third angle.
61°
Angles in a triangle sum to 180°: 180° − (46° + 73°) = 61°.
8. Two interior angles of a triangle measure 70° and 30°. Find the third angle.
80°
Angles in a triangle sum to 180°: 180° − (70° + 30°) = 80°.
9. Two interior angles of a triangle measure 45° and 52°. Find the third angle.
83°
Angles in a triangle sum to 180°: 180° − (45° + 52°) = 83°.
10. Two interior angles of a triangle measure 34° and 31°. Find the third angle.
115°
Angles in a triangle sum to 180°: 180° − (34° + 31°) = 115°.
11. Two interior angles of a triangle measure 35° and 49°. Find the third angle.
96°
Angles in a triangle sum to 180°: 180° − (35° + 49°) = 96°.
12. Two interior angles of a triangle measure 82° and 68°. Find the third angle.
30°
Angles in a triangle sum to 180°: 180° − (82° + 68°) = 30°.

12 questions · Seed 67 · 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 59° and 56°. Find the third angle.
59° · 56° · Missing triangle angles
2. Two interior angles of a triangle measure 48° and 36°. Find the third angle.
48° · 36° · Missing triangle angles
3. Two interior angles of a triangle measure 68° and 59°. Find the third angle.
68° · 59° · Missing triangle angles
4. Two interior angles of a triangle measure 58° and 26°. Find the third angle.
58° · 26° · Missing triangle angles
5. Two interior angles of a triangle measure 59° and 57°. Find the third angle.
59° · 57° · Missing triangle angles
6. Two interior angles of a triangle measure 81° and 65°. Find the third angle.
81° · 65° · Missing triangle angles
7. Two interior angles of a triangle measure 46° and 73°. Find the third angle.
46° · 73° · Missing triangle angles
8. Two interior angles of a triangle measure 70° and 30°. Find the third angle.
70° · 30° · Missing triangle angles
9. Two interior angles of a triangle measure 45° and 52°. Find the third angle.
45° · 52° · Missing triangle angles
10. Two interior angles of a triangle measure 34° and 31°. Find the third angle.
34° · 31° · Missing triangle angles
11. Two interior angles of a triangle measure 35° and 49°. Find the third angle.
35° · 49° · Missing triangle angles
12. Two interior angles of a triangle measure 82° and 68°. Find the third angle.
82° · 68° · Missing triangle angles

12 questions · Seed 67 · 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 59° and 56°. Find the third angle.
65°
Angles in a triangle sum to 180°: 180° − (59° + 56°) = 65°.
2. Two interior angles of a triangle measure 48° and 36°. Find the third angle.
96°
Angles in a triangle sum to 180°: 180° − (48° + 36°) = 96°.
3. 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°.
4. Two interior angles of a triangle measure 58° and 26°. Find the third angle.
96°
Angles in a triangle sum to 180°: 180° − (58° + 26°) = 96°.
5. Two interior angles of a triangle measure 59° and 57°. Find the third angle.
64°
Angles in a triangle sum to 180°: 180° − (59° + 57°) = 64°.
6. Two interior angles of a triangle measure 81° and 65°. Find the third angle.
34°
Angles in a triangle sum to 180°: 180° − (81° + 65°) = 34°.
7. Two interior angles of a triangle measure 46° and 73°. Find the third angle.
61°
Angles in a triangle sum to 180°: 180° − (46° + 73°) = 61°.
8. Two interior angles of a triangle measure 70° and 30°. Find the third angle.
80°
Angles in a triangle sum to 180°: 180° − (70° + 30°) = 80°.
9. Two interior angles of a triangle measure 45° and 52°. Find the third angle.
83°
Angles in a triangle sum to 180°: 180° − (45° + 52°) = 83°.
10. Two interior angles of a triangle measure 34° and 31°. Find the third angle.
115°
Angles in a triangle sum to 180°: 180° − (34° + 31°) = 115°.
11. Two interior angles of a triangle measure 35° and 49°. Find the third angle.
96°
Angles in a triangle sum to 180°: 180° − (35° + 49°) = 96°.
12. Two interior angles of a triangle measure 82° and 68°. Find the third angle.
30°
Angles in a triangle sum to 180°: 180° − (82° + 68°) = 30°.

12 questions · Seed 67 · Age guidance, not curriculum certification