Free Grade 3 Introducing Vertically Opposite Angles Common Errors Lessons
Free Grade 3 lessons for Introducing Vertically Opposite Angles 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
Foundation
30 min
24
Learning objectives
Every objective is checkable, and each one maps to an activity and an assessment.
- RememberIdentify introducing vertically opposite angles common errors
Identify introducing vertically opposite angles common errors accurately in a familiar context.
Assessed by: Exit ticket of four short items
- UnderstandExplain introducing vertically opposite angles common errors
Explain introducing vertically opposite angles common errors accurately in a familiar context.
Assessed by: Exit ticket of four short items
- ApplyCalculate introducing vertically opposite angles common errors
Calculate introducing vertically opposite angles common errors accurately in a familiar context.
Assessed by: Exit ticket of four short items
- AnalyseCompare introducing vertically opposite angles common errors
Compare introducing vertically opposite angles 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 Introducing Vertically Opposite Angles 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 74°. Find the other.[1]
- 2.Two angles on a straight line. One is 61°. Find the other.[1]
- 3.Two angles on a straight line. One is 130°. Find the other.[1]
- 4.Two angles on a straight line. One is 55°. Find the other.[1]
- 5.A triangle has angles 78° and 68°. Find the third angle.[2]
- 6.A triangle has angles 74° and 85°. Find the third angle.[2]
- 7.A triangle has angles 36° and 68°. Find the third angle.[2]
- 8.A triangle has angles 35° and 117°. Find the third angle.[2]
- 9.Find the size of each interior angle of a regular 6-sided polygon.[3]
- 10.Find the size of each interior angle of a regular 8-sided polygon.[3]
- 11.Find the size of each interior angle of a regular 10-sided polygon.[3]
- 12.Find the size of each interior angle of a regular 7-sided polygon.[3]
Show answers and working
1. 106°
Angles on a straight line add to 180°. 180 − 74 = 106°.
2. 119°
Angles on a straight line add to 180°. 180 − 61 = 119°.
3. 50°
Angles on a straight line add to 180°. 180 − 130 = 50°.
4. 125°
Angles on a straight line add to 180°. 180 − 55 = 125°.
5. 34°
Angles in a triangle add to 180°. 180 − 78 − 68 = 34°.
6. 21°
Angles in a triangle add to 180°. 180 − 74 − 85 = 21°.
7. 76°
Angles in a triangle add to 180°. 180 − 36 − 68 = 76°.
8. 28°
Angles in a triangle add to 180°. 180 − 35 − 117 = 28°.
9. 120°
Sum of interior angles = (6 − 2) × 180 = 720°. Each angle = 720 ÷ 6 = 120°.
10. 135°
Sum of interior angles = (8 − 2) × 180 = 1080°. Each angle = 1080 ÷ 8 = 135°.
11. 144°
Sum of interior angles = (10 − 2) × 180 = 1440°. Each angle = 1440 ÷ 10 = 144°.
12. 128.57°
Sum of interior angles = (7 − 2) × 180 = 900°. Each angle = 900 ÷ 7 = 128.57°.
Worked examples
Two angles on a straight line. One is 136°. Find the other.
- Angles on a straight line add to 180°.
- 180 − 136 = 44°.
- Answer: 44°
A triangle has angles 75° and 46°. Find the third angle.
- Angles in a triangle add to 180°.
- 180 − 75 − 46 = 59°.
- Answer: 59°
Find the size of each interior angle of a regular 9-sided polygon.
- Sum of interior angles = (9 − 2) × 180 = 1260°.
- Each angle = 1260 ÷ 9 = 140°.
- Answer: 140°
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 Vertically Opposite Angles Word Problems, Introducing Vertically Opposite Angles Techniques, Angles Around a Point. Each one has its own free lesson, worksheet and quiz.
- How is the lesson 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 Introducing Vertically Opposite Angles Common Errors?
- Move on to Working with Vertically Opposite Angles, Vertically Opposite Angles in Context, which build directly on this idea.
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