Today is rung 4 of 4 on this topic
Area, surface area and nets
Can do: Finds the area of triangles, parallelograms and composite shapes, and surface area from a net.
Why it matters
It moves geometry from a memorised formula list to reasoning about shapes — decomposing, rearranging, unfolding.
What it looks like when it's wobbly
Forgets to halve for a triangle, uses a slanted side as the height, and confuses surface area with volume.
⏱️ Two-minute check
"Area of a triangle with base 8 and height 5? Surface area of a 2×3×4 box?"
Solid looks like: 20 and 52, with units.
The full activity for this topic · 25 minutes
Cut, Unfold, Measure
- 1Cut a rectangle diagonally and see the two identical triangles — that's why we halve.
- 2Cut a parallelogram and rearrange it into a rectangle. Same area, easier shape.
- 3Unfold a cereal box completely flat. That's a net.
- 4Measure every face and total them for the surface area, then check for the pairs.
- 5Split an L-shaped room into rectangles and find its area.
If it's too hard
Rectangles and right triangles only.
If it's too easy
Composite 3-D shapes, and finding a missing dimension from a given area.
Say this
"The height has to be straight up from the base — not the slanted side. Where's the right angle?"