Grade 5 · Math · Lesson 21

Area and Perimeter (Composite Shapes)

Area is the amount of flat space a shape covers, measured in SQUARE units. Perimeter is the total distance around the outside of a shape, measured in plain units. In the US we measure rooms in feet and small objects in inches; in metric science work we use centimeters and meters. The formulas are exactly the same — only the unit labels change. Composite shapes are made of two or more rectangles joined together — once you split them apart, the work becomes ordinary rectangle math in whichever units the problem gives.

What this lesson teaches

1Compute the area of a rectangle by multiplying length times width in both customary units (sq in, sq ft) and metric units (cm², m²)
2Compute the perimeter of a rectangle by adding every outer side in inches, feet, centimeters, or meters
3Decompose a composite figure into non-overlapping rectangles to find total area in either unit system
4Find the perimeter of a composite figure by adding the lengths of all outer edges in either inches/feet or cm/meters

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