Free Grade 3 Angles in Parallel Lines in Context Common Errors Lesson Plans
Free Grade 3 lesson plans for Angles in Parallel Lines in Context Common Errors: 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
25 min
24
Learning objectives
Every objective is checkable, and each one maps to an activity and an assessment.
- RememberIdentify angles in parallel lines in context common errors
Identify angles in parallel lines in context common errors accurately in a familiar context.
Assessed by: Exit ticket of four short items
- UnderstandExplain angles in parallel lines in context common errors
Explain angles in parallel lines in context common errors accurately in a familiar context.
Assessed by: Exit ticket of four short items
- ApplyCalculate angles in parallel lines in context common errors
Calculate angles in parallel lines in context common errors accurately in a familiar context.
Assessed by: Exit ticket of four short items
- AnalyseCompare angles in parallel lines in context common errors
Compare angles in parallel lines in context common errors 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 Angles in Parallel Lines in Context Common Errors 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 155°. Find the other.[1]
- 2.Two angles on a straight line. One is 132°. Find the other.[1]
- 3.Two angles on a straight line. One is 149°. Find the other.[1]
- 4.Two angles on a straight line. One is 33°. Find the other.[1]
- 5.A triangle has angles 54° and 66°. Find the third angle.[2]
- 6.A triangle has angles 30° and 58°. Find the third angle.[2]
- 7.A triangle has angles 75° and 73°. Find the third angle.[2]
- 8.A triangle has angles 56° and 21°. 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 10-sided polygon.[3]
- 11.Find the size of each interior angle of a regular 9-sided polygon.[3]
- 12.Find the size of each interior angle of a regular 6-sided polygon.[3]
Show answers and working
1. 25°
Angles on a straight line add to 180°. 180 − 155 = 25°.
2. 48°
Angles on a straight line add to 180°. 180 − 132 = 48°.
3. 31°
Angles on a straight line add to 180°. 180 − 149 = 31°.
4. 147°
Angles on a straight line add to 180°. 180 − 33 = 147°.
5. 60°
Angles in a triangle add to 180°. 180 − 54 − 66 = 60°.
6. 92°
Angles in a triangle add to 180°. 180 − 30 − 58 = 92°.
7. 32°
Angles in a triangle add to 180°. 180 − 75 − 73 = 32°.
8. 103°
Angles in a triangle add to 180°. 180 − 56 − 21 = 103°.
9. 135°
Sum of interior angles = (8 − 2) × 180 = 1080°. Each angle = 1080 ÷ 8 = 135°.
10. 144°
Sum of interior angles = (10 − 2) × 180 = 1440°. Each angle = 1440 ÷ 10 = 144°.
11. 140°
Sum of interior angles = (9 − 2) × 180 = 1260°. Each angle = 1260 ÷ 9 = 140°.
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 133°. Find the other.
- Angles on a straight line add to 180°.
- 180 − 133 = 47°.
- Answer: 47°
A triangle has angles 55° and 41°. Find the third angle.
- Angles in a triangle add to 180°.
- 180 − 55 − 41 = 84°.
- Answer: 84°
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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- Start with Angles in Parallel Lines in Context Word Problems, Angles in Parallel Lines in Context Techniques, Working with Angles in Parallel Lines. Each one has its own free lesson, worksheet and quiz.
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- Move on to Introducing Angles in Parallel Lines, Working with Angles in Parallel Lines, which build directly on this idea.
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