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An overhead tank fills on the terrace. How many buckets does it hold?

This track builds the ideas behind Class 9 surface area and volume.

What you will learn

• A box unrolled — six rectangles, added for the outside.
• A box filled — the same box, counted in cubes.
• Two growth stories — double an edge, and the two counts grow differently.
• A tin unrolled — a label that peels into one flat rectangle.
• The cone and its slant — the slant comes from a right triangle.
• Round all the way — the sphere, and the hemisphere's new face.
• A pyramid of canvas — walls use the slant.
• Which measure the job wants — skin (outside) or filling (inside).

Quick catch-up

A few earlier ideas help here.

• A solid's faces fold flat into a net.
• A rectangle's area is side times side.
• A cube number stacks unit cubes with no gaps.
• Right triangles — the longest side squared equals the other two squares added.

Two questions come up again and again. How much covers a solid? How much fills it? Ask which one the question wants.