Understand the rule first
Perimeter measures the boundary, area measures a flat surface and volume measures three-dimensional space. Compound shapes can be split into rectangles without overlap.
Distinguish perimeter, area and volume and calculate each with correct units.
Perimeter measures the boundary, area measures a flat surface and volume measures three-dimensional space. Compound shapes can be split into rectangles without overlap.
Using the same formula or units for perimeter, area and volume.
Reusable method: Write the required measure and units before choosing a formula.Find the side length whose square is 81.
Answer A: 36 cm
The side is 9 cm, so the perimeter is 4 × 9 = 36 cm.
Quick method: Write the required measure and units before choosing a formula.
Use one half × base × perpendicular height.
Answer B: 42 cm²
12 × 7 ÷ 2 = 42 cm².
Quick method: Write the required measure and units before choosing a formula.
Multiply all three dimensions.
Answer C: 72 cm³
6 × 4 × 3 = 72 cm³.
Quick method: Write the required measure and units before choosing a formula.
Subtract the small rectangular area from the large one.
Answer D: 74 cm²
10 × 8 − 3 × 2 = 80 − 6 = 74 cm².
Quick method: Write the required measure and units before choosing a formula.
Multiply the edge length three times.
Answer A: 125 cm³
5 × 5 × 5 = 125 cm³.
Quick method: Write the required measure and units before choosing a formula.
Add two lengths and two widths.
Answer D: 26 cm
Perimeter = 2 × (8 + 5) = 26 cm.
Quick method: Write the required measure and units before choosing a formula.
Use one half × base × height.
Answer A: 42 cm²
Area = 1/2 × 12 × 7 = 42 cm².
Quick method: Write the required measure and units before choosing a formula.
Multiply all three dimensions.
Answer B: 72 cm³
6 × 4 × 3 = 72 cm³.
Quick method: Write the required measure and units before choosing a formula.
Find the large area, then subtract the cut-out.
Answer C: 68 cm²
10 × 8 = 80 cm² and 4 × 3 = 12 cm². The L-shape area is 80 − 12 = 68 cm².
Quick method: Write the required measure and units before choosing a formula.
Divide the volume by the base area.
Answer D: 6 cm
The base area is 12 × 5 = 60 cm². Height = 360 ÷ 60 = 6 cm.
Quick method: Write the required measure and units before choosing a formula.