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 47° and 66°. Find the third angle.
47° · 66° · Missing triangle angles
2. Two interior angles of a triangle measure 69° and 65°. Find the third angle.
69° · 65° · Missing triangle angles
3. Two interior angles of a triangle measure 76° and 71°. Find the third angle.
76° · 71° · Missing triangle angles
4. Two interior angles of a triangle measure 29° and 44°. Find the third angle.
29° · 44° · Missing triangle angles
5. Two interior angles of a triangle measure 38° and 64°. Find the third angle.
38° · 64° · Missing triangle angles
6. Two interior angles of a triangle measure 41° and 46°. Find the third angle.
41° · 46° · Missing triangle angles
7. Two interior angles of a triangle measure 45° and 28°. Find the third angle.
45° · 28° · Missing triangle angles
8. Two interior angles of a triangle measure 45° and 36°. Find the third angle.
45° · 36° · Missing triangle angles
9. Two interior angles of a triangle measure 28° and 43°. Find the third angle.
28° · 43° · Missing triangle angles
10. Two interior angles of a triangle measure 26° and 60°. Find the third angle.
26° · 60° · Missing triangle angles
11. Two interior angles of a triangle measure 64° and 68°. Find the third angle.
64° · 68° · Missing triangle angles
12. Two interior angles of a triangle measure 39° and 57°. Find the third angle.
39° · 57° · Missing triangle angles

12 questions · Seed 50 · 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 47° and 66°. Find the third angle.
67°
Angles in a triangle sum to 180°: 180° − (47° + 66°) = 67°.
2. Two interior angles of a triangle measure 69° and 65°. Find the third angle.
46°
Angles in a triangle sum to 180°: 180° − (69° + 65°) = 46°.
3. Two interior angles of a triangle measure 76° and 71°. Find the third angle.
33°
Angles in a triangle sum to 180°: 180° − (76° + 71°) = 33°.
4. Two interior angles of a triangle measure 29° and 44°. Find the third angle.
107°
Angles in a triangle sum to 180°: 180° − (29° + 44°) = 107°.
5. Two interior angles of a triangle measure 38° and 64°. Find the third angle.
78°
Angles in a triangle sum to 180°: 180° − (38° + 64°) = 78°.
6. Two interior angles of a triangle measure 41° and 46°. Find the third angle.
93°
Angles in a triangle sum to 180°: 180° − (41° + 46°) = 93°.
7. Two interior angles of a triangle measure 45° and 28°. Find the third angle.
107°
Angles in a triangle sum to 180°: 180° − (45° + 28°) = 107°.
8. Two interior angles of a triangle measure 45° and 36°. Find the third angle.
99°
Angles in a triangle sum to 180°: 180° − (45° + 36°) = 99°.
9. Two interior angles of a triangle measure 28° and 43°. Find the third angle.
109°
Angles in a triangle sum to 180°: 180° − (28° + 43°) = 109°.
10. Two interior angles of a triangle measure 26° and 60°. Find the third angle.
94°
Angles in a triangle sum to 180°: 180° − (26° + 60°) = 94°.
11. Two interior angles of a triangle measure 64° and 68°. Find the third angle.
48°
Angles in a triangle sum to 180°: 180° − (64° + 68°) = 48°.
12. Two interior angles of a triangle measure 39° and 57°. Find the third angle.
84°
Angles in a triangle sum to 180°: 180° − (39° + 57°) = 84°.

12 questions · Seed 50 · 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 47° and 66°. Find the third angle.
47° · 66° · Missing triangle angles
2. Two interior angles of a triangle measure 69° and 65°. Find the third angle.
69° · 65° · Missing triangle angles
3. Two interior angles of a triangle measure 76° and 71°. Find the third angle.
76° · 71° · Missing triangle angles
4. Two interior angles of a triangle measure 29° and 44°. Find the third angle.
29° · 44° · Missing triangle angles
5. Two interior angles of a triangle measure 38° and 64°. Find the third angle.
38° · 64° · Missing triangle angles
6. Two interior angles of a triangle measure 41° and 46°. Find the third angle.
41° · 46° · Missing triangle angles
7. Two interior angles of a triangle measure 45° and 28°. Find the third angle.
45° · 28° · Missing triangle angles
8. Two interior angles of a triangle measure 45° and 36°. Find the third angle.
45° · 36° · Missing triangle angles
9. Two interior angles of a triangle measure 28° and 43°. Find the third angle.
28° · 43° · Missing triangle angles
10. Two interior angles of a triangle measure 26° and 60°. Find the third angle.
26° · 60° · Missing triangle angles
11. Two interior angles of a triangle measure 64° and 68°. Find the third angle.
64° · 68° · Missing triangle angles
12. Two interior angles of a triangle measure 39° and 57°. Find the third angle.
39° · 57° · Missing triangle angles

12 questions · Seed 50 · 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 47° and 66°. Find the third angle.
67°
Angles in a triangle sum to 180°: 180° − (47° + 66°) = 67°.
2. Two interior angles of a triangle measure 69° and 65°. Find the third angle.
46°
Angles in a triangle sum to 180°: 180° − (69° + 65°) = 46°.
3. Two interior angles of a triangle measure 76° and 71°. Find the third angle.
33°
Angles in a triangle sum to 180°: 180° − (76° + 71°) = 33°.
4. Two interior angles of a triangle measure 29° and 44°. Find the third angle.
107°
Angles in a triangle sum to 180°: 180° − (29° + 44°) = 107°.
5. Two interior angles of a triangle measure 38° and 64°. Find the third angle.
78°
Angles in a triangle sum to 180°: 180° − (38° + 64°) = 78°.
6. Two interior angles of a triangle measure 41° and 46°. Find the third angle.
93°
Angles in a triangle sum to 180°: 180° − (41° + 46°) = 93°.
7. Two interior angles of a triangle measure 45° and 28°. Find the third angle.
107°
Angles in a triangle sum to 180°: 180° − (45° + 28°) = 107°.
8. Two interior angles of a triangle measure 45° and 36°. Find the third angle.
99°
Angles in a triangle sum to 180°: 180° − (45° + 36°) = 99°.
9. Two interior angles of a triangle measure 28° and 43°. Find the third angle.
109°
Angles in a triangle sum to 180°: 180° − (28° + 43°) = 109°.
10. Two interior angles of a triangle measure 26° and 60°. Find the third angle.
94°
Angles in a triangle sum to 180°: 180° − (26° + 60°) = 94°.
11. Two interior angles of a triangle measure 64° and 68°. Find the third angle.
48°
Angles in a triangle sum to 180°: 180° − (64° + 68°) = 48°.
12. Two interior angles of a triangle measure 39° and 57°. Find the third angle.
84°
Angles in a triangle sum to 180°: 180° − (39° + 57°) = 84°.

12 questions · Seed 50 · Age guidance, not curriculum certification