Area of Triangle
Pair a base with the height perpendicular to it, then halve base times height to find the area.
Your child learns that any side of a triangle can be the base, and that the height is the line meeting that base at a right angle, even outside the triangle. Two equal triangles make a rectangle, so one triangle is 1/2 × base × height. Your child then finds areas of composite figures, triangles inside rectangles, and two identical shapes that overlap. Read the study guide →
About this chapter
Primary 5 area of triangle questions start with base and height: which side is the base, and which line is the height that belongs to it. From there the chapter finds the area of a triangle and of composite figures made of rectangles, squares and triangles.
Practise by question type: p5 area of a triangle questions, p5 base and height of a triangle questions, p5 triangles inside a rectangle questions, p5 overlapping shapes area questions and p5 area of composite figures.
The order to learn them
Which base and perpendicular height go together?
5.1 and 5.2
A triangle can use any side as its base. Its matching height meets that base at a right angle.
Composite figures and equal areas
5.3 to 5.5
Split a composite figure into rectangles, squares and triangles. Count each part once.
The number tells you where a question type sits in this chapter, not what your child needs to learn first. A child who has already met a type in school can practise it without working through the ones above it.
How the end-of-year papers set these questions
Triangle questions appear throughout the Primary 5 papers.
The 2025 Primary 5 end-of-year papers include direct area calculations, questions that ask for a base or height, and composite figures made from rectangles, squares and triangles.
The printed figure is part of the question.
A short item may ask for one perpendicular height. Longer questions often require a missing measurement to be found before any area is calculated. A printed length may belong to the whole figure rather than to the triangle being used.
The questions are modelled against top school papers.
We used the 2025 Primary 5 end-of-year papers to check the question types and the written working. Every practice question is original, and no school question is reproduced.
Everything here is modelled against top school papers. Those papers are never reproduced, and every question on this site is original.
How to set out the working clearly
These examples show Mathweave's clear, consistent layout for each method. The layout is informed by the answer keys we reviewed.
- Name the base and height before calculating Mark the chosen base and the perpendicular height that belongs with it. Extend the base when the perpendicular meets the line outside the triangle.
- Write the triangle rule before substituting measurements State the triangle rule as part of the calculation. Mathweave places area of a triangle = 1/2 × base × height on a line before substituting the measurements. The base and height must be the pair already identified on the figure.
- Find missing measurements on their own lines When a side belongs to a larger rectangle or square, write the subtraction that finds the triangle's measurement before using the area rule. Keep one derived value on each line.
- Name every part added or subtracted For a composite figure, state the shape or region used on each line. If two identical shapes overlap, add both whole shapes and subtract one copy of the shared region.
Questions parents ask
Is this the Primary 5 syllabus?
The chapter follows the latest MOE Primary Mathematics syllabus. It covers base and height, the area of a triangle and composite figures made from rectangles, squares and triangles.
Can any side of a triangle be the base?
Yes. Each choice of base has its own perpendicular height. The pair must meet at a right angle, even when the height falls outside the triangle.
Why do two lesson pages say Primary 5 and Primary 6?
Triangles inside a rectangle and two overlapping shapes are shared types. Each has one lesson page with the level line Primary 5 and Primary 6.
Are the questions from past papers?
We write the questions ourselves rather than copy them from papers. Each chapter is modelled on the types of question that top school papers set. A question may look like one your child has met before because it is the same type.
Primary 5 area of a triangle questions by question type
Primary 5 Area of Triangle Study Guide
Turn a triangle to try each base, cut two triangles into a rectangle and slide a tip along a box. Five steps, worked examples and a five-question check.
Start hereBase and heightArea of a triangleComposite figuresTriangle in a rectangleOverlapping shapesOpen the study guide →