Free Grade 3 Working with Triangles Worksheets
Free Grade 3 worksheets for Working with Triangles: 12 real questions with a full answer key and worked solutions. Angles on a straight line add to 180°, around a point to 360°, and inside a triangle to 180°. A polygon with n sides has interior angles adding to (n − 2) × 180°.
Free
Core
25 min
24
Learning objectives
Every objective is checkable, and each one maps to an activity and an assessment.
- UnderstandExplain working with triangles
Explain working with triangles accurately in a familiar context.
Assessed by: Exit ticket of four short items
- ApplyCalculate working with triangles
Calculate working with triangles accurately in a familiar context.
Assessed by: Exit ticket of four short items
- AnalyseCompare working with triangles
Compare working with triangles accurately in a familiar context.
Assessed by: Exit ticket of four short items
- EvaluateJustify working with triangles
Justify working with triangles accurately in a familiar context.
Assessed by: Exit ticket of four short items
Prerequisites
Close these gaps first — each has its own free lesson, worksheet and quiz.
How Working with Triangles works
Angles on a straight line add to 180°, around a point to 360°, and inside a triangle to 180°. A polygon with n sides has interior angles adding to (n − 2) × 180°.
12 practice questions
Easy to hard, 24 marks in total. Try them first, then open the answers.
- 1.Two angles on a straight line. One is 149°. Find the other.[1]
- 2.Two angles on a straight line. One is 152°. Find the other.[1]
- 3.Two angles on a straight line. One is 47°. Find the other.[1]
- 4.Two angles on a straight line. One is 88°. Find the other.[1]
- 5.A triangle has angles 75° and 25°. Find the third angle.[2]
- 6.A triangle has angles 34° and 115°. Find the third angle.[2]
- 7.A triangle has angles 86° and 59°. Find the third angle.[2]
- 8.A triangle has angles 68° and 77°. Find the third angle.[2]
- 9.Find the size of each interior angle of a regular 8-sided polygon.[3]
- 10.Find the size of each interior angle of a regular 6-sided polygon.[3]
- 11.Find the size of each interior angle of a regular 7-sided polygon.[3]
- 12.Find the size of each interior angle of a regular 5-sided polygon.[3]
Show answers and working
1. 31°
Angles on a straight line add to 180°. 180 − 149 = 31°.
2. 28°
Angles on a straight line add to 180°. 180 − 152 = 28°.
3. 133°
Angles on a straight line add to 180°. 180 − 47 = 133°.
4. 92°
Angles on a straight line add to 180°. 180 − 88 = 92°.
5. 80°
Angles in a triangle add to 180°. 180 − 75 − 25 = 80°.
6. 31°
Angles in a triangle add to 180°. 180 − 34 − 115 = 31°.
7. 35°
Angles in a triangle add to 180°. 180 − 86 − 59 = 35°.
8. 35°
Angles in a triangle add to 180°. 180 − 68 − 77 = 35°.
9. 135°
Sum of interior angles = (8 − 2) × 180 = 1080°. Each angle = 1080 ÷ 8 = 135°.
10. 120°
Sum of interior angles = (6 − 2) × 180 = 720°. Each angle = 720 ÷ 6 = 120°.
11. 128.57°
Sum of interior angles = (7 − 2) × 180 = 900°. Each angle = 900 ÷ 7 = 128.57°.
12. 108°
Sum of interior angles = (5 − 2) × 180 = 540°. Each angle = 540 ÷ 5 = 108°.
Worked examples
Two angles on a straight line. One is 74°. Find the other.
- Angles on a straight line add to 180°.
- 180 − 74 = 106°.
- Answer: 106°
A triangle has angles 23° and 132°. Find the third angle.
- Angles in a triangle add to 180°.
- 180 − 23 − 132 = 25°.
- Answer: 25°
Find the size of each interior angle of a regular 10-sided polygon.
- Sum of interior angles = (10 − 2) × 180 = 1440°.
- Each angle = 1440 ÷ 10 = 144°.
- Answer: 144°
Interactive practice
Free, no account required — answer on screen or print it.
Common mistakes
What learners typically get wrong, and how to fix it.
Reads the wrong scale on a protractor.
Correction: Start from the 0 on the arm you are measuring from.
Uses 360° for a triangle.
Correction: Triangle = 180°, quadrilateral = 360°.
Teacher tips
- · Estimate the angle type before measuring.
Parent tips
- · Spot right angles around the house.
Real-life applications
- · Ramps, clock hands, building and design.
Assessment objectives
How mastery is evidenced, and which standards it maps to.
Every free resource for Working with Triangles
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Frequently asked
- Is this Grade 3 Working with Triangles worksheet really free?
- Yes. Every worksheets on FreeMathWorksheet is free to use, print and share — no account, no paywall and no watermark.
- What should a learner already know before this?
- Start with Introducing Triangles, Angles. Each one has its own free lesson, worksheet and quiz.
- How is the worksheet sequenced?
- Recognition first, then understanding, application, reasoning and finally mastery — the same ladder used across every free resource on the platform.
- What comes next after Working with Triangles?
- Move on to Triangles in Context, Quadrilaterals, Circles, Polygons, which build directly on this idea.
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