Understand the idea.
Look for smaller pieces
A composite shape joins simpler flat shapes into one figure. Look for a place to draw a dividing line so that each piece is familiar. In the house outline, the dashed line separates a triangular roof from a rectangular lower part.
Describe how the pieces join, as well as their names. The pieces meet along an edge with no gap. A dividing line helps describe the shape; it does not change the shape’s outside boundary.
Flat shapes and solid objects
Flat shapes have length and width. Solids also have depth. A drawing of a tower is flat, but the model it represents may be made from a cylinder body and a cone top. Use names that describe the actual pieces.
Check properties rather than guessing from a familiar object’s name. A triangle has three straight sides; a cylinder has two circular flat faces and a curved surface. More than one sensible division may describe a composite object.
See the method in action.
A house shape
Describe the two shapes in the supplied house outline.
Worked solution
- 1
Use the dividing line.
The dashed line separates the supplied house outline into an upper and a lower piece.
- 2
Name the upper piece.
Its three straight sides identify a triangle.
- 3
Name the lower piece and the arrangement.
The lower piece has four right angles, so the complete shape is a triangle above a rectangle.
A triangle above a rectangle.
A model tower
A model has a cylinder body with a cone placed on top. Which two solids form it?
Worked solution
- 1
Identify the body as a solid.
The model body has depth and is stated to be a cylinder, rather than a flat rectangle or circle.
- 2
Identify the top as a solid.
The pointed piece is a cone, with a circular base and curved surface meeting at a point.
- 3
Describe the combined object.
A cone placed on a cylinder gives the two solid components of the model tower.
A cylinder and a cone.
Try it yourself.
Check your understanding
A shape is made by placing two squares side by side along a full edge. What overall shape is formed?
Show answer & reasoning
A rectangle.
The outside outline is a rectangle: it has four right angles and two longer opposite sides. The shared edge lies inside the joined shape, so it does not make an extra outside side.
Keep practising
6 worksheet questions · 9 marks
Read the questions online
- Name the two component shapes shown in the house diagram.1 mark
- Two identical squares are joined along one full edge. Name the outside shape.1 mark
- A toy is made from one cube body and one pyramid roof. Name its two solid pieces.1 mark
- Can a rectangle be split into two triangles? Describe a line that does this.2 marks
- A student calls a cylinder-and-cone tower “a circle and a triangle”. Explain what is missing.2 marks
- Draw one composite shape made from two rectangles. Show the join.2 marks
Read the worked solutions
Equivalent correct methods earn the corresponding marks. Include units where asked.
- Name the two component shapes shown in the house diagram.1 mark
The dashed line separates the three-sided roof from the rectangular body.
A triangle and a rectangle. - Two identical squares are joined along one full edge. Name the outside shape.1 mark
The shared edge is inside the combined shape.
A rectangle. - A toy is made from one cube body and one pyramid roof. Name its two solid pieces.1 mark
Both pieces have depth, so use solid names.
A cube and a pyramid. - Can a rectangle be split into two triangles? Describe a line that does this.2 marks
The diagonal divides the rectangle into two three-sided parts.
Yes. Draw a diagonal joining opposite corners. - A student calls a cylinder-and-cone tower “a circle and a triangle”. Explain what is missing.2 marks
The tower has depth.
The names describe flat shapes, not the solid pieces. Use cylinder and cone. - Draw one composite shape made from two rectangles. Show the join.2 marks
The two rectangles touch along an edge without overlapping. Other valid drawings are possible.
One valid answer is an L-shape made from a tall rectangle and a shorter rectangle beside its bottom.
Curriculum reference & lesson scope
Australian Curriculum v9 / SA Curriculum Mathematics 2026
Composite shapes/objects; angle names; reflection/rotational symmetry; creating designs.
Official curriculum source ↗