Skip to content
Auralith
Log inGet started

Year 7 · Maths · Calculating with numbers · Lesson 3

Perimeter

Find perimeters of rectangles, squares, regular polygons and rectilinear shapes, including missing sides and reverse problems.

Whiteboard video lesson: Perimeter

25-minute video lesson

Teaching, worked examples and 20 practice questions solved step by step.

Watch free for a month

What your child will learn

  • Understand perimeter
  • Find the perimeter of rectangles and squares
  • Find missing sides of rectilinear shapes
  • Find a missing side from the perimeter
  • Solve perimeter problems

The method

  1. Find any missing sides first.
  2. Missing horizontal side: use the other horizontal sides.
  3. Missing vertical side: use the other vertical sides.
  4. Add ALL the sides; tick them off as you go.

Key words: perimeter, rectangle, rectilinear, side, length.

Worked examples

The first three practice questions from the lesson, with every step.

Question 1

Find the perimeter of a rectangle 6 cm by 3 cm.

  1. Step 1: Sketch it
  2. Step 2: 6 + 3 + 6 + 3 = 18 cm
  3. Step 3: (or 2 × (6 + 3) = 18)

Answer: 18 cm

Question 2

Find the perimeter of a rectangle 12 cm by 5 cm.

  1. Step 1: Sketch it
  2. Step 2: 12 + 5 + 12 + 5 = 34 cm
  3. Step 3: (or 2 × (12 + 5) = 34)

Answer: 34 cm

Question 3

Find the perimeter of a rectangle 7.5 cm by 4 cm.

  1. Step 1: Sketch it
  2. Step 2: 7.5 + 4 + 7.5 + 4 = 23 cm
  3. Step 3: (or 2 × (7.5 + 4) = 23)

Answer: 23 cm