Angles in a triangle
Name: _____________________ Date: __________
Show your thinking with numbers, words, or a drawing.
1. Find the missing angle in the triangle, marked with a question mark. The diagram is not drawn to scale.
2. Find the missing angle in the triangle, marked with a question mark. The diagram is not drawn to scale.
3. Find the missing angle in the triangle, marked with a question mark. The diagram is not drawn to scale.
4. Find the missing angle in the triangle, marked with a question mark. The diagram is not drawn to scale.
5. Find the missing angle in the triangle, marked with a question mark. The diagram is not drawn to scale.
Answer key · Angles in a triangle
1. 30
The angles in a triangle add up to 180°.
Add the angles you know: 90 + 60 = 150.
180 − 150 = 30, so the missing angle is 30°.
2. 100
The angles in a triangle add up to 180°.
Add the angles you know: 30 + 50 = 80.
180 − 80 = 100, so the missing angle is 100°.
3. 75
The angles in a triangle add up to 180°.
Add the angles you know: 40 + 65 = 105.
180 − 105 = 75, so the missing angle is 75°.
4. 50
The angles in a triangle add up to 180°.
Add the angles you know: 55 + 75 = 130.
180 − 130 = 50, so the missing angle is 50°.
5. 105
The angles in a triangle add up to 180°.
Add the angles you know: 25 + 50 = 75.
180 − 75 = 105, so the missing angle is 105°.
Try it together
Choose a question from the printable. Use objects or a drawing to show your thinking, then explain your method to someone at home.