Free Grade 3 Working with Introducing Triangles Common Errors Flashcards
Free Grade 3 flashcards for Working with Introducing Triangles 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°.
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35 min
24
Learning objectives
Every objective is checkable, and each one maps to an activity and an assessment.
- RememberIdentify working with introducing triangles common errors
Identify working with introducing triangles common errors accurately in a familiar context.
Assessed by: Exit ticket of four short items
- UnderstandExplain working with introducing triangles common errors
Explain working with introducing triangles common errors accurately in a familiar context.
Assessed by: Exit ticket of four short items
- ApplyCalculate working with introducing triangles common errors
Calculate working with introducing triangles common errors accurately in a familiar context.
Assessed by: Exit ticket of four short items
- AnalyseCompare working with introducing triangles common errors
Compare working with introducing triangles 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 Working with Introducing Triangles 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 105°. Find the other.[1]
- 2.Two angles on a straight line. One is 134°. Find the other.[1]
- 3.Two angles on a straight line. One is 42°. Find the other.[1]
- 4.Two angles on a straight line. One is 52°. Find the other.[1]
- 5.A triangle has angles 63° and 79°. Find the third angle.[2]
- 6.A triangle has angles 78° and 53°. Find the third angle.[2]
- 7.A triangle has angles 48° and 49°. Find the third angle.[2]
- 8.A triangle has angles 79° and 64°. Find the third angle.[2]
- 9.Find the size of each interior angle of a regular 9-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 6-sided polygon.[3]
- 12.Find the size of each interior angle of a regular 7-sided polygon.[3]
Show answers and working
1. 75°
Angles on a straight line add to 180°. 180 − 105 = 75°.
2. 46°
Angles on a straight line add to 180°. 180 − 134 = 46°.
3. 138°
Angles on a straight line add to 180°. 180 − 42 = 138°.
4. 128°
Angles on a straight line add to 180°. 180 − 52 = 128°.
5. 38°
Angles in a triangle add to 180°. 180 − 63 − 79 = 38°.
6. 49°
Angles in a triangle add to 180°. 180 − 78 − 53 = 49°.
7. 83°
Angles in a triangle add to 180°. 180 − 48 − 49 = 83°.
8. 37°
Angles in a triangle add to 180°. 180 − 79 − 64 = 37°.
9. 140°
Sum of interior angles = (9 − 2) × 180 = 1260°. Each angle = 1260 ÷ 9 = 140°.
10. 144°
Sum of interior angles = (10 − 2) × 180 = 1440°. Each angle = 1440 ÷ 10 = 144°.
11. 120°
Sum of interior angles = (6 − 2) × 180 = 720°. Each angle = 720 ÷ 6 = 120°.
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 47°. Find the other.
- Angles on a straight line add to 180°.
- 180 − 47 = 133°.
- Answer: 133°
A triangle has angles 70° and 62°. Find the third angle.
- Angles in a triangle add to 180°.
- 180 − 70 − 62 = 48°.
- Answer: 48°
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
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- Start with Rules and Methods in Introducing Triangles Common Errors, Key Vocabulary of Introducing Triangles Common Errors, Introducing Triangles Word Problems. Each one has its own free lesson, worksheet and quiz.
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- Move on to Introducing Triangles Common Errors in Examinations, Introducing Triangles Essentials, Introducing Triangles Techniques, Introducing Triangles Word Problems, which build directly on this idea.
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