Solid shapes · Usually met around P5
Properties of 3D shapes
Count the base's sides, then work it out.
How to do it
Method
Count the base's sides, then work it out
Hexagonal prism's edges: 6 × 3 = 18
Another way
Count them
6 + 6 + 6 = 18
In full
A prism has two matching bases, top and bottom, with rectangles round the sides. A pyramid has one base, with triangles round the sides that meet at a point at the top. A base with 6 sides makes a hexagonal prism or pyramid. A cube and a cuboid are four-sided prisms. When you count faces, edges and vertices, count the hidden ones (the dashed lines) too. Quicker: count the sides of the base, then work it out. For a prism: faces = sides + 2, edges = sides × 3, vertices = sides × 2. For a pyramid: faces = sides + 1, edges = sides × 2, vertices = sides + 1. A hexagonal prism's edges: 6 × 3 = 18. A pentagonal pyramid's faces: 5 + 1 = 6. A cuboid's vertices: 4 × 2 = 8. Another way is to count them one by one. A hexagonal prism has 6 edges on top, 6 at the bottom and 6 up the sides: 6 + 6 + 6 = 18.
Worked examples
Have a go first, then open each one for the answer and the working.
Example 1
A cuboid has ? faces
Show the answer and working
Answer: A cuboid has 6 faces
A cuboid has 2 bases and 4 faces round the side: 4 + 2 = 6, so 6 faces
Example 2
A triangular prism has ? edges
Show the answer and working
Answer: A triangular prism has 9 edges
The top and the bottom have 3 edges each, and 3 more run up the side: 3 × 3 = 9, so 9 edges
Example 3
A hexagonal pyramid has ? edges
Show the answer and working
Answer: A hexagonal pyramid has 12 edges
The base has 6 edges, and one runs from the top to each corner of it: 6 × 2 = 12, so 12 edges
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