Measure and calculate the perimeter of composite rectilinear shapes in centimetres and metres - Reasoning

When delving into the topic of measuring and calculating the perimeter of composite rectilinear shapes, students are encouraged to apply their understanding of geometry to more complex figures. A composite rectilinear shape is essentially a shape made up of multiple rectangles or squares joined together. To determine the perimeter of such a shape, one must measure the length of all the outer sides. The task requires careful consideration to ensure that all external sides are accounted for, particularly in shapes where sides are shared between the constituent rectangles or squares. The measurements can be taken in centimetres or metres, depending on the scale of the shape and the level of precision required.

In terms of reasoning, students must be able to articulate their process for finding the perimeter and justify their method. They need to explain why certain lengths are measured and others are not—typically, internal dividing lines are not included in the perimeter calculation. The reasoning aspect of this task not only tests students' ability to perform the necessary calculations but also their comprehension of the concept of perimeter as it applies to composite shapes. This skill is crucial for solving real-world problems, such as determining the amount of material needed to fence a garden or frame a piece of artwork composed of several shapes.