Free Grade 3 Working with Angles in Parallel Lines Essentials Lessons
Free Grade 3 lessons for Working with Angles in Parallel Lines Essentials: 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
Higher
30 min
24
Learning objectives
Every objective is checkable, and each one maps to an activity and an assessment.
- RememberIdentify working with angles in parallel lines essentials
Identify working with angles in parallel lines essentials accurately in a familiar context.
Assessed by: Exit ticket of four short items
- UnderstandExplain working with angles in parallel lines essentials
Explain working with angles in parallel lines essentials accurately in a familiar context.
Assessed by: Exit ticket of four short items
- ApplyCalculate working with angles in parallel lines essentials
Calculate working with angles in parallel lines essentials accurately in a familiar context.
Assessed by: Exit ticket of four short items
- AnalyseCompare working with angles in parallel lines essentials
Compare working with angles in parallel lines essentials 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 Angles in Parallel Lines Essentials 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 104°. Find the other.[1]
- 2.Two angles on a straight line. One is 85°. Find the other.[1]
- 3.Two angles on a straight line. One is 109°. Find the other.[1]
- 4.Two angles on a straight line. One is 93°. Find the other.[1]
- 5.A triangle has angles 78° and 26°. Find the third angle.[2]
- 6.A triangle has angles 78° and 80°. Find the third angle.[2]
- 7.A triangle has angles 64° and 64°. Find the third angle.[2]
- 8.A triangle has angles 59° and 53°. Find the third angle.[2]
- 9.Find the size of each interior angle of a regular 10-sided polygon.[3]
- 10.Find the size of each interior angle of a regular 9-sided polygon.[3]
- 11.Find the size of each interior angle of a regular 5-sided polygon.[3]
- 12.Find the size of each interior angle of a regular 6-sided polygon.[3]
Show answers and working
1. 76°
Angles on a straight line add to 180°. 180 − 104 = 76°.
2. 95°
Angles on a straight line add to 180°. 180 − 85 = 95°.
3. 71°
Angles on a straight line add to 180°. 180 − 109 = 71°.
4. 87°
Angles on a straight line add to 180°. 180 − 93 = 87°.
5. 76°
Angles in a triangle add to 180°. 180 − 78 − 26 = 76°.
6. 22°
Angles in a triangle add to 180°. 180 − 78 − 80 = 22°.
7. 52°
Angles in a triangle add to 180°. 180 − 64 − 64 = 52°.
8. 68°
Angles in a triangle add to 180°. 180 − 59 − 53 = 68°.
9. 144°
Sum of interior angles = (10 − 2) × 180 = 1440°. Each angle = 1440 ÷ 10 = 144°.
10. 140°
Sum of interior angles = (9 − 2) × 180 = 1260°. Each angle = 1260 ÷ 9 = 140°.
11. 108°
Sum of interior angles = (5 − 2) × 180 = 540°. Each angle = 540 ÷ 5 = 108°.
12. 120°
Sum of interior angles = (6 − 2) × 180 = 720°. Each angle = 720 ÷ 6 = 120°.
Worked examples
Two angles on a straight line. One is 125°. Find the other.
- Angles on a straight line add to 180°.
- 180 − 125 = 55°.
- Answer: 55°
A triangle has angles 68° and 55°. Find the third angle.
- Angles in a triangle add to 180°.
- 180 − 68 − 55 = 57°.
- Answer: 57°
Find the size of each interior angle of a regular 7-sided polygon.
- Sum of interior angles = (7 − 2) × 180 = 900°.
- Each angle = 900 ÷ 7 = 128.57°.
- Answer: 128.57°
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.
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Frequently asked
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- What should a learner already know before this?
- Start with Introducing Angles in Parallel Lines. Each one has its own free lesson, worksheet and quiz.
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- 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 Angles in Parallel Lines Essentials?
- Move on to Working with Angles in Parallel Lines Techniques, Working with Angles in Parallel Lines Word Problems, Working with Angles in Parallel Lines Common Errors, Introducing Angles in Parallel Lines, which build directly on this idea.
Related resources
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