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 64° and 42°. Find the third angle.
64° · 42° · Missing triangle angles
2. Two interior angles of a triangle measure 32° and 47°. Find the third angle.
32° · 47° · Missing triangle angles
3. Two interior angles of a triangle measure 54° and 44°. Find the third angle.
54° · 44° · Missing triangle angles
4. Two interior angles of a triangle measure 72° and 51°. Find the third angle.
72° · 51° · Missing triangle angles
5. Two interior angles of a triangle measure 60° and 27°. Find the third angle.
60° · 27° · Missing triangle angles
6. Two interior angles of a triangle measure 61° and 39°. Find the third angle.
61° · 39° · Missing triangle angles
7. Two interior angles of a triangle measure 65° and 38°. Find the third angle.
65° · 38° · Missing triangle angles
8. Two interior angles of a triangle measure 64° and 39°. Find the third angle.
64° · 39° · Missing triangle angles
9. Two interior angles of a triangle measure 33° and 35°. Find the third angle.
33° · 35° · Missing triangle angles
10. Two interior angles of a triangle measure 49° and 61°. Find the third angle.
49° · 61° · Missing triangle angles
11. Two interior angles of a triangle measure 44° and 31°. Find the third angle.
44° · 31° · Missing triangle angles
12. Two interior angles of a triangle measure 36° and 26°. Find the third angle.
36° · 26° · Missing triangle angles

12 questions · Seed 104741 · 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 64° and 42°. Find the third angle.
74°
Angles in a triangle sum to 180°: 180° − (64° + 42°) = 74°.
2. Two interior angles of a triangle measure 32° and 47°. Find the third angle.
101°
Angles in a triangle sum to 180°: 180° − (32° + 47°) = 101°.
3. Two interior angles of a triangle measure 54° and 44°. Find the third angle.
82°
Angles in a triangle sum to 180°: 180° − (54° + 44°) = 82°.
4. Two interior angles of a triangle measure 72° and 51°. Find the third angle.
57°
Angles in a triangle sum to 180°: 180° − (72° + 51°) = 57°.
5. Two interior angles of a triangle measure 60° and 27°. Find the third angle.
93°
Angles in a triangle sum to 180°: 180° − (60° + 27°) = 93°.
6. Two interior angles of a triangle measure 61° and 39°. Find the third angle.
80°
Angles in a triangle sum to 180°: 180° − (61° + 39°) = 80°.
7. Two interior angles of a triangle measure 65° and 38°. Find the third angle.
77°
Angles in a triangle sum to 180°: 180° − (65° + 38°) = 77°.
8. 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°.
9. Two interior angles of a triangle measure 33° and 35°. Find the third angle.
112°
Angles in a triangle sum to 180°: 180° − (33° + 35°) = 112°.
10. Two interior angles of a triangle measure 49° and 61°. Find the third angle.
70°
Angles in a triangle sum to 180°: 180° − (49° + 61°) = 70°.
11. Two interior angles of a triangle measure 44° and 31°. Find the third angle.
105°
Angles in a triangle sum to 180°: 180° − (44° + 31°) = 105°.
12. Two interior angles of a triangle measure 36° and 26°. Find the third angle.
118°
Angles in a triangle sum to 180°: 180° − (36° + 26°) = 118°.

12 questions · Seed 104741 · 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 64° and 42°. Find the third angle.
64° · 42° · Missing triangle angles
2. Two interior angles of a triangle measure 32° and 47°. Find the third angle.
32° · 47° · Missing triangle angles
3. Two interior angles of a triangle measure 54° and 44°. Find the third angle.
54° · 44° · Missing triangle angles
4. Two interior angles of a triangle measure 72° and 51°. Find the third angle.
72° · 51° · Missing triangle angles
5. Two interior angles of a triangle measure 60° and 27°. Find the third angle.
60° · 27° · Missing triangle angles
6. Two interior angles of a triangle measure 61° and 39°. Find the third angle.
61° · 39° · Missing triangle angles
7. Two interior angles of a triangle measure 65° and 38°. Find the third angle.
65° · 38° · Missing triangle angles
8. Two interior angles of a triangle measure 64° and 39°. Find the third angle.
64° · 39° · Missing triangle angles
9. Two interior angles of a triangle measure 33° and 35°. Find the third angle.
33° · 35° · Missing triangle angles
10. Two interior angles of a triangle measure 49° and 61°. Find the third angle.
49° · 61° · Missing triangle angles
11. Two interior angles of a triangle measure 44° and 31°. Find the third angle.
44° · 31° · Missing triangle angles
12. Two interior angles of a triangle measure 36° and 26°. Find the third angle.
36° · 26° · Missing triangle angles

12 questions · Seed 104741 · 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 64° and 42°. Find the third angle.
74°
Angles in a triangle sum to 180°: 180° − (64° + 42°) = 74°.
2. Two interior angles of a triangle measure 32° and 47°. Find the third angle.
101°
Angles in a triangle sum to 180°: 180° − (32° + 47°) = 101°.
3. Two interior angles of a triangle measure 54° and 44°. Find the third angle.
82°
Angles in a triangle sum to 180°: 180° − (54° + 44°) = 82°.
4. Two interior angles of a triangle measure 72° and 51°. Find the third angle.
57°
Angles in a triangle sum to 180°: 180° − (72° + 51°) = 57°.
5. Two interior angles of a triangle measure 60° and 27°. Find the third angle.
93°
Angles in a triangle sum to 180°: 180° − (60° + 27°) = 93°.
6. Two interior angles of a triangle measure 61° and 39°. Find the third angle.
80°
Angles in a triangle sum to 180°: 180° − (61° + 39°) = 80°.
7. Two interior angles of a triangle measure 65° and 38°. Find the third angle.
77°
Angles in a triangle sum to 180°: 180° − (65° + 38°) = 77°.
8. 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°.
9. Two interior angles of a triangle measure 33° and 35°. Find the third angle.
112°
Angles in a triangle sum to 180°: 180° − (33° + 35°) = 112°.
10. Two interior angles of a triangle measure 49° and 61°. Find the third angle.
70°
Angles in a triangle sum to 180°: 180° − (49° + 61°) = 70°.
11. Two interior angles of a triangle measure 44° and 31°. Find the third angle.
105°
Angles in a triangle sum to 180°: 180° − (44° + 31°) = 105°.
12. Two interior angles of a triangle measure 36° and 26°. Find the third angle.
118°
Angles in a triangle sum to 180°: 180° − (36° + 26°) = 118°.

12 questions · Seed 104741 · Age guidance, not curriculum certification