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 31° and 27°. Find the third angle.
31° · 27° · Missing triangle angles
2. Two interior angles of a triangle measure 44° and 73°. Find the third angle.
44° · 73° · Missing triangle angles
3. Two interior angles of a triangle measure 62° and 70°. Find the third angle.
62° · 70° · Missing triangle angles
4. Two interior angles of a triangle measure 50° and 62°. Find the third angle.
50° · 62° · Missing triangle angles
5. Two interior angles of a triangle measure 77° and 56°. Find the third angle.
77° · 56° · Missing triangle angles
6. Two interior angles of a triangle measure 70° and 54°. Find the third angle.
70° · 54° · Missing triangle angles
7. Two interior angles of a triangle measure 82° and 34°. Find the third angle.
82° · 34° · Missing triangle angles
8. Two interior angles of a triangle measure 36° and 66°. Find the third angle.
36° · 66° · Missing triangle angles
9. Two interior angles of a triangle measure 64° and 39°. Find the third angle.
64° · 39° · Missing triangle angles
10. Two interior angles of a triangle measure 38° and 66°. Find the third angle.
38° · 66° · Missing triangle angles
11. Two interior angles of a triangle measure 32° and 68°. Find the third angle.
32° · 68° · Missing triangle angles
12. Two interior angles of a triangle measure 65° and 47°. Find the third angle.
65° · 47° · Missing triangle angles

12 questions · Seed 42 · 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 31° and 27°. Find the third angle.
122°
Angles in a triangle sum to 180°: 180° − (31° + 27°) = 122°.
2. Two interior angles of a triangle measure 44° and 73°. Find the third angle.
63°
Angles in a triangle sum to 180°: 180° − (44° + 73°) = 63°.
3. Two interior angles of a triangle measure 62° and 70°. Find the third angle.
48°
Angles in a triangle sum to 180°: 180° − (62° + 70°) = 48°.
4. Two interior angles of a triangle measure 50° and 62°. Find the third angle.
68°
Angles in a triangle sum to 180°: 180° − (50° + 62°) = 68°.
5. Two interior angles of a triangle measure 77° and 56°. Find the third angle.
47°
Angles in a triangle sum to 180°: 180° − (77° + 56°) = 47°.
6. Two interior angles of a triangle measure 70° and 54°. Find the third angle.
56°
Angles in a triangle sum to 180°: 180° − (70° + 54°) = 56°.
7. Two interior angles of a triangle measure 82° and 34°. Find the third angle.
64°
Angles in a triangle sum to 180°: 180° − (82° + 34°) = 64°.
8. Two interior angles of a triangle measure 36° and 66°. Find the third angle.
78°
Angles in a triangle sum to 180°: 180° − (36° + 66°) = 78°.
9. Two interior angles of a triangle measure 64° and 39°. Find the third angle.
77°
Angles in a triangle sum to 180°: 180° − (64° + 39°) = 77°.
10. Two interior angles of a triangle measure 38° and 66°. Find the third angle.
76°
Angles in a triangle sum to 180°: 180° − (38° + 66°) = 76°.
11. Two interior angles of a triangle measure 32° and 68°. Find the third angle.
80°
Angles in a triangle sum to 180°: 180° − (32° + 68°) = 80°.
12. Two interior angles of a triangle measure 65° and 47°. Find the third angle.
68°
Angles in a triangle sum to 180°: 180° − (65° + 47°) = 68°.

12 questions · Seed 42 · 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 31° and 27°. Find the third angle.
31° · 27° · Missing triangle angles
2. Two interior angles of a triangle measure 44° and 73°. Find the third angle.
44° · 73° · Missing triangle angles
3. Two interior angles of a triangle measure 62° and 70°. Find the third angle.
62° · 70° · Missing triangle angles
4. Two interior angles of a triangle measure 50° and 62°. Find the third angle.
50° · 62° · Missing triangle angles
5. Two interior angles of a triangle measure 77° and 56°. Find the third angle.
77° · 56° · Missing triangle angles
6. Two interior angles of a triangle measure 70° and 54°. Find the third angle.
70° · 54° · Missing triangle angles
7. Two interior angles of a triangle measure 82° and 34°. Find the third angle.
82° · 34° · Missing triangle angles
8. Two interior angles of a triangle measure 36° and 66°. Find the third angle.
36° · 66° · Missing triangle angles
9. Two interior angles of a triangle measure 64° and 39°. Find the third angle.
64° · 39° · Missing triangle angles
10. Two interior angles of a triangle measure 38° and 66°. Find the third angle.
38° · 66° · Missing triangle angles
11. Two interior angles of a triangle measure 32° and 68°. Find the third angle.
32° · 68° · Missing triangle angles
12. Two interior angles of a triangle measure 65° and 47°. Find the third angle.
65° · 47° · Missing triangle angles

12 questions · Seed 42 · 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 31° and 27°. Find the third angle.
122°
Angles in a triangle sum to 180°: 180° − (31° + 27°) = 122°.
2. Two interior angles of a triangle measure 44° and 73°. Find the third angle.
63°
Angles in a triangle sum to 180°: 180° − (44° + 73°) = 63°.
3. Two interior angles of a triangle measure 62° and 70°. Find the third angle.
48°
Angles in a triangle sum to 180°: 180° − (62° + 70°) = 48°.
4. Two interior angles of a triangle measure 50° and 62°. Find the third angle.
68°
Angles in a triangle sum to 180°: 180° − (50° + 62°) = 68°.
5. Two interior angles of a triangle measure 77° and 56°. Find the third angle.
47°
Angles in a triangle sum to 180°: 180° − (77° + 56°) = 47°.
6. Two interior angles of a triangle measure 70° and 54°. Find the third angle.
56°
Angles in a triangle sum to 180°: 180° − (70° + 54°) = 56°.
7. Two interior angles of a triangle measure 82° and 34°. Find the third angle.
64°
Angles in a triangle sum to 180°: 180° − (82° + 34°) = 64°.
8. Two interior angles of a triangle measure 36° and 66°. Find the third angle.
78°
Angles in a triangle sum to 180°: 180° − (36° + 66°) = 78°.
9. Two interior angles of a triangle measure 64° and 39°. Find the third angle.
77°
Angles in a triangle sum to 180°: 180° − (64° + 39°) = 77°.
10. Two interior angles of a triangle measure 38° and 66°. Find the third angle.
76°
Angles in a triangle sum to 180°: 180° − (38° + 66°) = 76°.
11. Two interior angles of a triangle measure 32° and 68°. Find the third angle.
80°
Angles in a triangle sum to 180°: 180° − (32° + 68°) = 80°.
12. Two interior angles of a triangle measure 65° and 47°. Find the third angle.
68°
Angles in a triangle sum to 180°: 180° − (65° + 47°) = 68°.

12 questions · Seed 42 · Age guidance, not curriculum certification