Free Grade 3 Area of a Triangle Flashcards
Free Grade 3 flashcards for Area of a Triangle: 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
35 min
24
Learning objectives
Every objective is checkable, and each one maps to an activity and an assessment.
- UnderstandExplain area of a triangle
Explain area of a triangle accurately in a familiar context.
Assessed by: Exit ticket of four short items
- ApplyCalculate area of a triangle
Calculate area of a triangle accurately in a familiar context.
Assessed by: Exit ticket of four short items
- AnalyseCompare area of a triangle
Compare area of a triangle accurately in a familiar context.
Assessed by: Exit ticket of four short items
- EvaluateJustify area of a triangle
Justify area of a triangle 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 Area of a Triangle 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 69°. Find the other.[1]
- 2.Two angles on a straight line. One is 133°. Find the other.[1]
- 3.Two angles on a straight line. One is 103°. Find the other.[1]
- 4.Two angles on a straight line. One is 127°. Find the other.[1]
- 5.A triangle has angles 88° and 62°. Find the third angle.[2]
- 6.A triangle has angles 85° and 60°. Find the third angle.[2]
- 7.A triangle has angles 81° and 46°. Find the third angle.[2]
- 8.A triangle has angles 69° and 51°. Find the third angle.[2]
- 9.Find the size of each interior angle of a regular 7-sided polygon.[3]
- 10.Find the size of each interior angle of a regular 5-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 8-sided polygon.[3]
Show answers and working
1. 111°
Angles on a straight line add to 180°. 180 − 69 = 111°.
2. 47°
Angles on a straight line add to 180°. 180 − 133 = 47°.
3. 77°
Angles on a straight line add to 180°. 180 − 103 = 77°.
4. 53°
Angles on a straight line add to 180°. 180 − 127 = 53°.
5. 30°
Angles in a triangle add to 180°. 180 − 88 − 62 = 30°.
6. 35°
Angles in a triangle add to 180°. 180 − 85 − 60 = 35°.
7. 53°
Angles in a triangle add to 180°. 180 − 81 − 46 = 53°.
8. 60°
Angles in a triangle add to 180°. 180 − 69 − 51 = 60°.
9. 128.57°
Sum of interior angles = (7 − 2) × 180 = 900°. Each angle = 900 ÷ 7 = 128.57°.
10. 108°
Sum of interior angles = (5 − 2) × 180 = 540°. Each angle = 540 ÷ 5 = 108°.
11. 140°
Sum of interior angles = (9 − 2) × 180 = 1260°. Each angle = 1260 ÷ 9 = 140°.
12. 135°
Sum of interior angles = (8 − 2) × 180 = 1080°. Each angle = 1080 ÷ 8 = 135°.
Worked examples
Two angles on a straight line. One is 82°. Find the other.
- Angles on a straight line add to 180°.
- 180 − 82 = 98°.
- Answer: 98°
A triangle has angles 83° and 74°. Find the third angle.
- Angles in a triangle add to 180°.
- 180 − 83 − 74 = 23°.
- Answer: 23°
Find the size of each interior angle of a regular 6-sided polygon.
- Sum of interior angles = (6 − 2) × 180 = 720°.
- Each angle = 720 ÷ 6 = 120°.
- Answer: 120°
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
- Is this Grade 3 Area of a Triangle flashcards really free?
- Yes. Every flashcards 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 Cosine Rule, Sine Rule, Right-angled Trigonometry. Each one has its own free lesson, worksheet and quiz.
- How is the flashcards 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 Area of a Triangle?
- Move on to Right-angled Trigonometry, Trigonometric Graphs, which build directly on this idea.
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