About this worksheet

This free Year 7 angle sum of a triangle worksheet is written for the Western Australian curriculum and mapped to SCSA content description WA7MMGTW6. It targets one skill so students can practise until it sticks: by the end, students can say “I can use the angle sum of a triangle and the exterior angle rule to find unknown angles and explain why the rule works.”

What’s inside

• Key idea box – a short explanation with worked examples to read before starting.
• A · Fluency (16 questions) – quick practice to build accuracy.
• B · Core (10 questions) – worded problems set in everyday Australian contexts.
• C · Reasoning (4 questions) – explain, justify and spot the error.
• D · Challenge (4 questions) – harder multi-step and problem-solving questions for students ready to stretch.
• Separate marking key – every answer with working, plus mark allocations and marking criteria for reasoning questions.

Skills covered

• Using the 180° angle sum to find unknown angles
• Using isosceles and equilateral triangle properties
• Applying the exterior angle rule

How to use this worksheet

Start with the Key idea box, then complete Section A without a calculator. Most students should attempt Sections B and C; Section D suits students aiming for the top of the class or preparing for accelerated or extension maths. The worksheet is marked out of 58, and the score box on the last page helps students see which section needs more practice.

Common mistakes to watch for

• Subtracting from 360° instead of 180°
• Forgetting that base angles of an isosceles triangle are equal
• Adding the wrong angles for an exterior angle
• Not checking the angles total 180°

Where this fits in the WA Year 7 sequence

Angle Sum of a Triangle sits in the Two-dimensional space and structures sub-strand of Measurement and geometry. It is one of a set of short, single-skill EduLift worksheets that split each Year 7 content description into sub-skills. Use the previous and next links to work through the sequence in order.

Common errors we see in tutoring

• Subtracting from 360° instead of 180°
• Forgetting that base angles of an isosceles triangle are equal
• Adding the wrong angles for an exterior angle
• Not checking the angles total 180°