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 43° and 63°. Find the third angle.
43° · 63° · Missing triangle angles
2. Two interior angles of a triangle measure 57° and 30°. Find the third angle.
57° · 30° · Missing triangle angles
3. Two interior angles of a triangle measure 44° and 73°. Find the third angle.
44° · 73° · Missing triangle angles
4. Two interior angles of a triangle measure 52° and 61°. Find the third angle.
52° · 61° · Missing triangle angles
5. Two interior angles of a triangle measure 43° and 25°. Find the third angle.
43° · 25° · Missing triangle angles
6. Two interior angles of a triangle measure 58° and 48°. Find the third angle.
58° · 48° · Missing triangle angles
7. Two interior angles of a triangle measure 60° and 27°. Find the third angle.
60° · 27° · Missing triangle angles
8. Two interior angles of a triangle measure 52° and 71°. Find the third angle.
52° · 71° · Missing triangle angles
9. Two interior angles of a triangle measure 65° and 53°. Find the third angle.
65° · 53° · Missing triangle angles
10. Two interior angles of a triangle measure 35° and 34°. Find the third angle.
35° · 34° · Missing triangle angles
11. Two interior angles of a triangle measure 53° and 53°. Find the third angle.
53° · 53° · Missing triangle angles
12. Two interior angles of a triangle measure 25° and 31°. Find the third angle.
25° · 31° · Missing triangle angles

12 questions · Seed 104740 · 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 43° and 63°. Find the third angle.
74°
Angles in a triangle sum to 180°: 180° − (43° + 63°) = 74°.
2. Two interior angles of a triangle measure 57° and 30°. Find the third angle.
93°
Angles in a triangle sum to 180°: 180° − (57° + 30°) = 93°.
3. 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°.
4. Two interior angles of a triangle measure 52° and 61°. Find the third angle.
67°
Angles in a triangle sum to 180°: 180° − (52° + 61°) = 67°.
5. Two interior angles of a triangle measure 43° and 25°. Find the third angle.
112°
Angles in a triangle sum to 180°: 180° − (43° + 25°) = 112°.
6. Two interior angles of a triangle measure 58° and 48°. Find the third angle.
74°
Angles in a triangle sum to 180°: 180° − (58° + 48°) = 74°.
7. 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°.
8. Two interior angles of a triangle measure 52° and 71°. Find the third angle.
57°
Angles in a triangle sum to 180°: 180° − (52° + 71°) = 57°.
9. Two interior angles of a triangle measure 65° and 53°. Find the third angle.
62°
Angles in a triangle sum to 180°: 180° − (65° + 53°) = 62°.
10. Two interior angles of a triangle measure 35° and 34°. Find the third angle.
111°
Angles in a triangle sum to 180°: 180° − (35° + 34°) = 111°.
11. Two interior angles of a triangle measure 53° and 53°. Find the third angle.
74°
Angles in a triangle sum to 180°: 180° − (53° + 53°) = 74°.
12. Two interior angles of a triangle measure 25° and 31°. Find the third angle.
124°
Angles in a triangle sum to 180°: 180° − (25° + 31°) = 124°.

12 questions · Seed 104740 · 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 43° and 63°. Find the third angle.
43° · 63° · Missing triangle angles
2. Two interior angles of a triangle measure 57° and 30°. Find the third angle.
57° · 30° · Missing triangle angles
3. Two interior angles of a triangle measure 44° and 73°. Find the third angle.
44° · 73° · Missing triangle angles
4. Two interior angles of a triangle measure 52° and 61°. Find the third angle.
52° · 61° · Missing triangle angles
5. Two interior angles of a triangle measure 43° and 25°. Find the third angle.
43° · 25° · Missing triangle angles
6. Two interior angles of a triangle measure 58° and 48°. Find the third angle.
58° · 48° · Missing triangle angles
7. Two interior angles of a triangle measure 60° and 27°. Find the third angle.
60° · 27° · Missing triangle angles
8. Two interior angles of a triangle measure 52° and 71°. Find the third angle.
52° · 71° · Missing triangle angles
9. Two interior angles of a triangle measure 65° and 53°. Find the third angle.
65° · 53° · Missing triangle angles
10. Two interior angles of a triangle measure 35° and 34°. Find the third angle.
35° · 34° · Missing triangle angles
11. Two interior angles of a triangle measure 53° and 53°. Find the third angle.
53° · 53° · Missing triangle angles
12. Two interior angles of a triangle measure 25° and 31°. Find the third angle.
25° · 31° · Missing triangle angles

12 questions · Seed 104740 · 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 43° and 63°. Find the third angle.
74°
Angles in a triangle sum to 180°: 180° − (43° + 63°) = 74°.
2. Two interior angles of a triangle measure 57° and 30°. Find the third angle.
93°
Angles in a triangle sum to 180°: 180° − (57° + 30°) = 93°.
3. 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°.
4. Two interior angles of a triangle measure 52° and 61°. Find the third angle.
67°
Angles in a triangle sum to 180°: 180° − (52° + 61°) = 67°.
5. Two interior angles of a triangle measure 43° and 25°. Find the third angle.
112°
Angles in a triangle sum to 180°: 180° − (43° + 25°) = 112°.
6. Two interior angles of a triangle measure 58° and 48°. Find the third angle.
74°
Angles in a triangle sum to 180°: 180° − (58° + 48°) = 74°.
7. 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°.
8. Two interior angles of a triangle measure 52° and 71°. Find the third angle.
57°
Angles in a triangle sum to 180°: 180° − (52° + 71°) = 57°.
9. Two interior angles of a triangle measure 65° and 53°. Find the third angle.
62°
Angles in a triangle sum to 180°: 180° − (65° + 53°) = 62°.
10. Two interior angles of a triangle measure 35° and 34°. Find the third angle.
111°
Angles in a triangle sum to 180°: 180° − (35° + 34°) = 111°.
11. Two interior angles of a triangle measure 53° and 53°. Find the third angle.
74°
Angles in a triangle sum to 180°: 180° − (53° + 53°) = 74°.
12. Two interior angles of a triangle measure 25° and 31°. Find the third angle.
124°
Angles in a triangle sum to 180°: 180° − (25° + 31°) = 124°.

12 questions · Seed 104740 · Age guidance, not curriculum certification