Teacher notes

• You may need to remind students to use their knowledge about the properties of shapes to calculate the perimeter of shapes where the lengths of some sides are not given. For example, symmetrical shapes like rectangles have opposite sides which are the same length, and the sides of regular shapes are always the same length.
• Encourage students to use multiplicative thinking for perimeters where multiple sides are the same length, rather than adding them all together.
  For example, a rectangle has two pairs of sides the same and so multiplication can be used to find the perimeter.
• Using a piece of string around the perimeter of a shape (including shapes with curved sides) will remind students that perimeter is a measurement of length.
• Encourage students to work systematically so they do not miss a side or count the same side twice, and also flexibly using efficient combinations. For example, some perimeters may be easiest to add using compatible sides, for others doubling or multiple sides of the same length may be the first step. For sides that contain fractions with the same denominator, it may be easiest to calculate the number of whole units, then combine fractions into whole units, and finally add to find the total. For example, 2 + 1 ½ + 2 + 1 ½ = (2 + 1 + 2 + 1) + (½ + ½) = 6 + 1 = 7 units.  Students should be able to justify the strategy they have used.