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 64° and 65°. Find the third angle.
64° · 65° · Missing triangle angles
2. Two interior angles of a triangle measure 26° and 54°. Find the third angle.
26° · 54° · Missing triangle angles
3. Two interior angles of a triangle measure 43° and 69°. Find the third angle.
43° · 69° · Missing triangle angles
4. Two interior angles of a triangle measure 32° and 25°. Find the third angle.
32° · 25° · Missing triangle angles
5. Two interior angles of a triangle measure 38° and 46°. Find the third angle.
38° · 46° · Missing triangle angles
6. Two interior angles of a triangle measure 81° and 72°. Find the third angle.
81° · 72° · Missing triangle angles
7. Two interior angles of a triangle measure 25° and 40°. Find the third angle.
25° · 40° · Missing triangle angles
8. Two interior angles of a triangle measure 31° and 57°. Find the third angle.
31° · 57° · Missing triangle angles
9. Two interior angles of a triangle measure 39° and 62°. Find the third angle.
39° · 62° · Missing triangle angles
10. Two interior angles of a triangle measure 36° and 29°. Find the third angle.
36° · 29° · Missing triangle angles
11. Two interior angles of a triangle measure 43° and 57°. Find the third angle.
43° · 57° · Missing triangle angles
12. Two interior angles of a triangle measure 80° and 59°. Find the third angle.
80° · 59° · Missing triangle angles

12 questions · Seed 104731 · 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 64° and 65°. Find the third angle.
51°
Angles in a triangle sum to 180°: 180° − (64° + 65°) = 51°.
2. Two interior angles of a triangle measure 26° and 54°. Find the third angle.
100°
Angles in a triangle sum to 180°: 180° − (26° + 54°) = 100°.
3. Two interior angles of a triangle measure 43° and 69°. Find the third angle.
68°
Angles in a triangle sum to 180°: 180° − (43° + 69°) = 68°.
4. Two interior angles of a triangle measure 32° and 25°. Find the third angle.
123°
Angles in a triangle sum to 180°: 180° − (32° + 25°) = 123°.
5. Two interior angles of a triangle measure 38° and 46°. Find the third angle.
96°
Angles in a triangle sum to 180°: 180° − (38° + 46°) = 96°.
6. Two interior angles of a triangle measure 81° and 72°. Find the third angle.
27°
Angles in a triangle sum to 180°: 180° − (81° + 72°) = 27°.
7. Two interior angles of a triangle measure 25° and 40°. Find the third angle.
115°
Angles in a triangle sum to 180°: 180° − (25° + 40°) = 115°.
8. Two interior angles of a triangle measure 31° and 57°. Find the third angle.
92°
Angles in a triangle sum to 180°: 180° − (31° + 57°) = 92°.
9. Two interior angles of a triangle measure 39° and 62°. Find the third angle.
79°
Angles in a triangle sum to 180°: 180° − (39° + 62°) = 79°.
10. Two interior angles of a triangle measure 36° and 29°. Find the third angle.
115°
Angles in a triangle sum to 180°: 180° − (36° + 29°) = 115°.
11. Two interior angles of a triangle measure 43° and 57°. Find the third angle.
80°
Angles in a triangle sum to 180°: 180° − (43° + 57°) = 80°.
12. Two interior angles of a triangle measure 80° and 59°. Find the third angle.
41°
Angles in a triangle sum to 180°: 180° − (80° + 59°) = 41°.

12 questions · Seed 104731 · 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 64° and 65°. Find the third angle.
64° · 65° · Missing triangle angles
2. Two interior angles of a triangle measure 26° and 54°. Find the third angle.
26° · 54° · Missing triangle angles
3. Two interior angles of a triangle measure 43° and 69°. Find the third angle.
43° · 69° · Missing triangle angles
4. Two interior angles of a triangle measure 32° and 25°. Find the third angle.
32° · 25° · Missing triangle angles
5. Two interior angles of a triangle measure 38° and 46°. Find the third angle.
38° · 46° · Missing triangle angles
6. Two interior angles of a triangle measure 81° and 72°. Find the third angle.
81° · 72° · Missing triangle angles
7. Two interior angles of a triangle measure 25° and 40°. Find the third angle.
25° · 40° · Missing triangle angles
8. Two interior angles of a triangle measure 31° and 57°. Find the third angle.
31° · 57° · Missing triangle angles
9. Two interior angles of a triangle measure 39° and 62°. Find the third angle.
39° · 62° · Missing triangle angles
10. Two interior angles of a triangle measure 36° and 29°. Find the third angle.
36° · 29° · Missing triangle angles
11. Two interior angles of a triangle measure 43° and 57°. Find the third angle.
43° · 57° · Missing triangle angles
12. Two interior angles of a triangle measure 80° and 59°. Find the third angle.
80° · 59° · Missing triangle angles

12 questions · Seed 104731 · 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 64° and 65°. Find the third angle.
51°
Angles in a triangle sum to 180°: 180° − (64° + 65°) = 51°.
2. Two interior angles of a triangle measure 26° and 54°. Find the third angle.
100°
Angles in a triangle sum to 180°: 180° − (26° + 54°) = 100°.
3. Two interior angles of a triangle measure 43° and 69°. Find the third angle.
68°
Angles in a triangle sum to 180°: 180° − (43° + 69°) = 68°.
4. Two interior angles of a triangle measure 32° and 25°. Find the third angle.
123°
Angles in a triangle sum to 180°: 180° − (32° + 25°) = 123°.
5. Two interior angles of a triangle measure 38° and 46°. Find the third angle.
96°
Angles in a triangle sum to 180°: 180° − (38° + 46°) = 96°.
6. Two interior angles of a triangle measure 81° and 72°. Find the third angle.
27°
Angles in a triangle sum to 180°: 180° − (81° + 72°) = 27°.
7. Two interior angles of a triangle measure 25° and 40°. Find the third angle.
115°
Angles in a triangle sum to 180°: 180° − (25° + 40°) = 115°.
8. Two interior angles of a triangle measure 31° and 57°. Find the third angle.
92°
Angles in a triangle sum to 180°: 180° − (31° + 57°) = 92°.
9. Two interior angles of a triangle measure 39° and 62°. Find the third angle.
79°
Angles in a triangle sum to 180°: 180° − (39° + 62°) = 79°.
10. Two interior angles of a triangle measure 36° and 29°. Find the third angle.
115°
Angles in a triangle sum to 180°: 180° − (36° + 29°) = 115°.
11. Two interior angles of a triangle measure 43° and 57°. Find the third angle.
80°
Angles in a triangle sum to 180°: 180° − (43° + 57°) = 80°.
12. Two interior angles of a triangle measure 80° and 59°. Find the third angle.
41°
Angles in a triangle sum to 180°: 180° − (80° + 59°) = 41°.

12 questions · Seed 104731 · Age guidance, not curriculum certification