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 47° and 70°. Find the third angle.
47° · 70° · Missing triangle angles
2. Two interior angles of a triangle measure 72° and 34°. Find the third angle.
72° · 34° · Missing triangle angles
3. Two interior angles of a triangle measure 70° and 44°. Find the third angle.
70° · 44° · Missing triangle angles
4. Two interior angles of a triangle measure 59° and 32°. Find the third angle.
59° · 32° · Missing triangle angles
5. Two interior angles of a triangle measure 32° and 74°. Find the third angle.
32° · 74° · Missing triangle angles
6. Two interior angles of a triangle measure 65° and 66°. Find the third angle.
65° · 66° · Missing triangle angles
7. Two interior angles of a triangle measure 26° and 55°. Find the third angle.
26° · 55° · Missing triangle angles
8. Two interior angles of a triangle measure 53° and 34°. Find the third angle.
53° · 34° · Missing triangle angles
9. Two interior angles of a triangle measure 41° and 75°. Find the third angle.
41° · 75° · Missing triangle angles
10. Two interior angles of a triangle measure 36° and 34°. Find the third angle.
36° · 34° · Missing triangle angles
11. Two interior angles of a triangle measure 33° and 44°. Find the third angle.
33° · 44° · Missing triangle angles
12. Two interior angles of a triangle measure 50° and 74°. Find the third angle.
50° · 74° · Missing triangle angles

12 questions · Seed 60 · 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 47° and 70°. Find the third angle.
63°
Angles in a triangle sum to 180°: 180° − (47° + 70°) = 63°.
2. Two interior angles of a triangle measure 72° and 34°. Find the third angle.
74°
Angles in a triangle sum to 180°: 180° − (72° + 34°) = 74°.
3. Two interior angles of a triangle measure 70° and 44°. Find the third angle.
66°
Angles in a triangle sum to 180°: 180° − (70° + 44°) = 66°.
4. Two interior angles of a triangle measure 59° and 32°. Find the third angle.
89°
Angles in a triangle sum to 180°: 180° − (59° + 32°) = 89°.
5. Two interior angles of a triangle measure 32° and 74°. Find the third angle.
74°
Angles in a triangle sum to 180°: 180° − (32° + 74°) = 74°.
6. Two interior angles of a triangle measure 65° and 66°. Find the third angle.
49°
Angles in a triangle sum to 180°: 180° − (65° + 66°) = 49°.
7. Two interior angles of a triangle measure 26° and 55°. Find the third angle.
99°
Angles in a triangle sum to 180°: 180° − (26° + 55°) = 99°.
8. Two interior angles of a triangle measure 53° and 34°. Find the third angle.
93°
Angles in a triangle sum to 180°: 180° − (53° + 34°) = 93°.
9. Two interior angles of a triangle measure 41° and 75°. Find the third angle.
64°
Angles in a triangle sum to 180°: 180° − (41° + 75°) = 64°.
10. Two interior angles of a triangle measure 36° and 34°. Find the third angle.
110°
Angles in a triangle sum to 180°: 180° − (36° + 34°) = 110°.
11. Two interior angles of a triangle measure 33° and 44°. Find the third angle.
103°
Angles in a triangle sum to 180°: 180° − (33° + 44°) = 103°.
12. Two interior angles of a triangle measure 50° and 74°. Find the third angle.
56°
Angles in a triangle sum to 180°: 180° − (50° + 74°) = 56°.

12 questions · Seed 60 · 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 47° and 70°. Find the third angle.
47° · 70° · Missing triangle angles
2. Two interior angles of a triangle measure 72° and 34°. Find the third angle.
72° · 34° · Missing triangle angles
3. Two interior angles of a triangle measure 70° and 44°. Find the third angle.
70° · 44° · Missing triangle angles
4. Two interior angles of a triangle measure 59° and 32°. Find the third angle.
59° · 32° · Missing triangle angles
5. Two interior angles of a triangle measure 32° and 74°. Find the third angle.
32° · 74° · Missing triangle angles
6. Two interior angles of a triangle measure 65° and 66°. Find the third angle.
65° · 66° · Missing triangle angles
7. Two interior angles of a triangle measure 26° and 55°. Find the third angle.
26° · 55° · Missing triangle angles
8. Two interior angles of a triangle measure 53° and 34°. Find the third angle.
53° · 34° · Missing triangle angles
9. Two interior angles of a triangle measure 41° and 75°. Find the third angle.
41° · 75° · Missing triangle angles
10. Two interior angles of a triangle measure 36° and 34°. Find the third angle.
36° · 34° · Missing triangle angles
11. Two interior angles of a triangle measure 33° and 44°. Find the third angle.
33° · 44° · Missing triangle angles
12. Two interior angles of a triangle measure 50° and 74°. Find the third angle.
50° · 74° · Missing triangle angles

12 questions · Seed 60 · 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 47° and 70°. Find the third angle.
63°
Angles in a triangle sum to 180°: 180° − (47° + 70°) = 63°.
2. Two interior angles of a triangle measure 72° and 34°. Find the third angle.
74°
Angles in a triangle sum to 180°: 180° − (72° + 34°) = 74°.
3. Two interior angles of a triangle measure 70° and 44°. Find the third angle.
66°
Angles in a triangle sum to 180°: 180° − (70° + 44°) = 66°.
4. Two interior angles of a triangle measure 59° and 32°. Find the third angle.
89°
Angles in a triangle sum to 180°: 180° − (59° + 32°) = 89°.
5. Two interior angles of a triangle measure 32° and 74°. Find the third angle.
74°
Angles in a triangle sum to 180°: 180° − (32° + 74°) = 74°.
6. Two interior angles of a triangle measure 65° and 66°. Find the third angle.
49°
Angles in a triangle sum to 180°: 180° − (65° + 66°) = 49°.
7. Two interior angles of a triangle measure 26° and 55°. Find the third angle.
99°
Angles in a triangle sum to 180°: 180° − (26° + 55°) = 99°.
8. Two interior angles of a triangle measure 53° and 34°. Find the third angle.
93°
Angles in a triangle sum to 180°: 180° − (53° + 34°) = 93°.
9. Two interior angles of a triangle measure 41° and 75°. Find the third angle.
64°
Angles in a triangle sum to 180°: 180° − (41° + 75°) = 64°.
10. Two interior angles of a triangle measure 36° and 34°. Find the third angle.
110°
Angles in a triangle sum to 180°: 180° − (36° + 34°) = 110°.
11. Two interior angles of a triangle measure 33° and 44°. Find the third angle.
103°
Angles in a triangle sum to 180°: 180° − (33° + 44°) = 103°.
12. Two interior angles of a triangle measure 50° and 74°. Find the third angle.
56°
Angles in a triangle sum to 180°: 180° − (50° + 74°) = 56°.

12 questions · Seed 60 · Age guidance, not curriculum certification