ReasoningAges 10-12

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 10-12

Missing triangle angles

Take your time. Show your thinking.

1. Two interior angles of a triangle measure 36° and 64°. Find the third angle.
36° · 64° · Missing triangle angles
2. Two interior angles of a triangle measure 47° and 33°. Find the third angle.
47° · 33° · Missing triangle angles
3. Two interior angles of a triangle measure 33° and 69°. Find the third angle.
33° · 69° · Missing triangle angles
4. Two interior angles of a triangle measure 51° and 32°. Find the third angle.
51° · 32° · Missing triangle angles
5. Two interior angles of a triangle measure 76° and 40°. Find the third angle.
76° · 40° · Missing triangle angles
6. Two interior angles of a triangle measure 75° and 59°. Find the third angle.
75° · 59° · Missing triangle angles
7. Two interior angles of a triangle measure 52° and 40°. Find the third angle.
52° · 40° · Missing triangle angles
8. Two interior angles of a triangle measure 61° and 25°. Find the third angle.
61° · 25° · Missing triangle angles
9. Two interior angles of a triangle measure 79° and 27°. Find the third angle.
79° · 27° · Missing triangle angles
10. Two interior angles of a triangle measure 69° and 30°. Find the third angle.
69° · 30° · Missing triangle angles
11. Two interior angles of a triangle measure 80° and 62°. Find the third angle.
80° · 62° · Missing triangle angles
12. Two interior angles of a triangle measure 74° and 46°. Find the third angle.
74° · 46° · Missing triangle angles

12 questions · Seed 52 · Age guidance, not curriculum certification

View the answer key

Worksheet StudioAnswer key · Ages 10-12

Missing triangle angles

Answers and reasoning. Review before teaching.

1. Two interior angles of a triangle measure 36° and 64°. Find the third angle.
80°
Angles in a triangle sum to 180°: 180° − (36° + 64°) = 80°.
2. Two interior angles of a triangle measure 47° and 33°. Find the third angle.
100°
Angles in a triangle sum to 180°: 180° − (47° + 33°) = 100°.
3. Two interior angles of a triangle measure 33° and 69°. Find the third angle.
78°
Angles in a triangle sum to 180°: 180° − (33° + 69°) = 78°.
4. Two interior angles of a triangle measure 51° and 32°. Find the third angle.
97°
Angles in a triangle sum to 180°: 180° − (51° + 32°) = 97°.
5. Two interior angles of a triangle measure 76° and 40°. Find the third angle.
64°
Angles in a triangle sum to 180°: 180° − (76° + 40°) = 64°.
6. Two interior angles of a triangle measure 75° and 59°. Find the third angle.
46°
Angles in a triangle sum to 180°: 180° − (75° + 59°) = 46°.
7. Two interior angles of a triangle measure 52° and 40°. Find the third angle.
88°
Angles in a triangle sum to 180°: 180° − (52° + 40°) = 88°.
8. Two interior angles of a triangle measure 61° and 25°. Find the third angle.
94°
Angles in a triangle sum to 180°: 180° − (61° + 25°) = 94°.
9. Two interior angles of a triangle measure 79° and 27°. Find the third angle.
74°
Angles in a triangle sum to 180°: 180° − (79° + 27°) = 74°.
10. Two interior angles of a triangle measure 69° and 30°. Find the third angle.
81°
Angles in a triangle sum to 180°: 180° − (69° + 30°) = 81°.
11. Two interior angles of a triangle measure 80° and 62°. Find the third angle.
38°
Angles in a triangle sum to 180°: 180° − (80° + 62°) = 38°.
12. Two interior angles of a triangle measure 74° and 46°. Find the third angle.
60°
Angles in a triangle sum to 180°: 180° − (74° + 46°) = 60°.

12 questions · Seed 52 · Age guidance, not curriculum certification

Worksheet StudioPractice pack · Ages 10-12

Missing triangle angles

Take your time. Show your thinking.

1. Two interior angles of a triangle measure 36° and 64°. Find the third angle.
36° · 64° · Missing triangle angles
2. Two interior angles of a triangle measure 47° and 33°. Find the third angle.
47° · 33° · Missing triangle angles
3. Two interior angles of a triangle measure 33° and 69°. Find the third angle.
33° · 69° · Missing triangle angles
4. Two interior angles of a triangle measure 51° and 32°. Find the third angle.
51° · 32° · Missing triangle angles
5. Two interior angles of a triangle measure 76° and 40°. Find the third angle.
76° · 40° · Missing triangle angles
6. Two interior angles of a triangle measure 75° and 59°. Find the third angle.
75° · 59° · Missing triangle angles
7. Two interior angles of a triangle measure 52° and 40°. Find the third angle.
52° · 40° · Missing triangle angles
8. Two interior angles of a triangle measure 61° and 25°. Find the third angle.
61° · 25° · Missing triangle angles
9. Two interior angles of a triangle measure 79° and 27°. Find the third angle.
79° · 27° · Missing triangle angles
10. Two interior angles of a triangle measure 69° and 30°. Find the third angle.
69° · 30° · Missing triangle angles
11. Two interior angles of a triangle measure 80° and 62°. Find the third angle.
80° · 62° · Missing triangle angles
12. Two interior angles of a triangle measure 74° and 46°. Find the third angle.
74° · 46° · Missing triangle angles

12 questions · Seed 52 · Age guidance, not curriculum certification

Worksheet StudioAnswer key · Ages 10-12

Missing triangle angles

Answers and reasoning. Review before teaching.

1. Two interior angles of a triangle measure 36° and 64°. Find the third angle.
80°
Angles in a triangle sum to 180°: 180° − (36° + 64°) = 80°.
2. Two interior angles of a triangle measure 47° and 33°. Find the third angle.
100°
Angles in a triangle sum to 180°: 180° − (47° + 33°) = 100°.
3. Two interior angles of a triangle measure 33° and 69°. Find the third angle.
78°
Angles in a triangle sum to 180°: 180° − (33° + 69°) = 78°.
4. Two interior angles of a triangle measure 51° and 32°. Find the third angle.
97°
Angles in a triangle sum to 180°: 180° − (51° + 32°) = 97°.
5. Two interior angles of a triangle measure 76° and 40°. Find the third angle.
64°
Angles in a triangle sum to 180°: 180° − (76° + 40°) = 64°.
6. Two interior angles of a triangle measure 75° and 59°. Find the third angle.
46°
Angles in a triangle sum to 180°: 180° − (75° + 59°) = 46°.
7. Two interior angles of a triangle measure 52° and 40°. Find the third angle.
88°
Angles in a triangle sum to 180°: 180° − (52° + 40°) = 88°.
8. Two interior angles of a triangle measure 61° and 25°. Find the third angle.
94°
Angles in a triangle sum to 180°: 180° − (61° + 25°) = 94°.
9. Two interior angles of a triangle measure 79° and 27°. Find the third angle.
74°
Angles in a triangle sum to 180°: 180° − (79° + 27°) = 74°.
10. Two interior angles of a triangle measure 69° and 30°. Find the third angle.
81°
Angles in a triangle sum to 180°: 180° − (69° + 30°) = 81°.
11. Two interior angles of a triangle measure 80° and 62°. Find the third angle.
38°
Angles in a triangle sum to 180°: 180° − (80° + 62°) = 38°.
12. Two interior angles of a triangle measure 74° and 46°. Find the third angle.
60°
Angles in a triangle sum to 180°: 180° − (74° + 46°) = 60°.

12 questions · Seed 52 · Age guidance, not curriculum certification