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📐 Topics & explainers · 6 min read

Geometry & Shapes for the Math Olympiad (Class 4 focus)

Geometry in the SOF IMO for Class 4: shapes, sides and corners, perimeter, the area-vs-perimeter mix-up, and two worked examples.

Geometry in the junior olympiad is not about proofs — it is about looking carefully. The IMO uses shapes to test whether a child can hold a definition precisely (is a square a rectangle?), count systematically (how many triangles hide in this figure?), and apply a formula in reverse (the perimeter is 36, so how long is one side?). School practice usually stops at the forward direction; olympiad questions love the reverse.

For Class 4, two clusters carry most of the marks: knowing shapes and their properties, and perimeter. Perimeter questions in particular are a favourite of the Everyday Mathematics section — fencing a garden, framing a picture, running around a playground.

What your child needs to know

  • Names and properties of basic shapes: sides, corners, and what makes a square special among rectangles.
  • Open and closed figures, and straight versus curved sides.
  • Perimeter as the total distance around a closed figure — add up all the sides.
  • The shortcuts: perimeter of a rectangle is 2 × (length + width); of a square, 4 × side.
  • Working backwards: finding a side when the perimeter is given.
  • Counting shapes inside composite figures without missing or double-counting.

Where children lose marks

  • Mixing perimeter with area: for a 12 cm by 7 cm rectangle, 12 × 7 = 84 is the area, not the perimeter — and 84 will always be one of the options.
  • Adding only two sides of a rectangle: 12 + 7 = 19 instead of going all the way around.
  • Forgetting units, or mixing them: a question that gives one side in metres and another in centimetres is testing attention, not geometry.
  • Counting only the obvious shapes in a figure: the big triangle made of four small ones is easy to miss.

✏️ Try it: perimeter of a rectangle (Class 4 level)

A rectangular garden is 12 m long and 7 m wide. What length of fence is needed to go all the way around it?

  1. A19 m
  2. B26 m
  3. C38 m
  4. D84 m
Show the answer

Answer: 38 m. A fence goes around the garden, so we need the perimeter: 2 × (12 + 7) = 2 × 19 = 38 m. The trap options are all real mistakes: 19 is only two sides, 26 is 12 + 7 + 7 (three sides), and 84 is 12 × 7 — the area, which measures the grass inside, not the fence around it.

✏️ Try it: working backwards (Class 4 level)

The perimeter of a square playground is 36 m. How long is each side?

  1. A6 m
  2. B9 m
  3. C12 m
  4. D18 m
Show the answer

Answer: 9 m. A square has 4 equal sides, so each side is 36 ÷ 4 = 9 m. Check forwards: 4 × 9 = 36. ✓ The option 6 comes from confusing this with 36 = 6 × 6 (a square number, not a square’s perimeter), and 18 from halving instead of quartering.

LittleMathematicians covers Class 4 geometry as game levels on shapes and perimeter, complete with diagram questions like the real paper, adapting to your child’s mastery as accuracy grows. It is free during early access — and if the dashboard shows perimeter lagging behind shapes, that is exactly where the next level will focus.

Practice this the fun way

Adaptive levels, exam-pattern mocks and progress you can see — free during early access.

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Keep reading

Basic shapes for Class 4: sides, corners, faces and edgesA Class 4 explainer of 2D and 3D shapes — counting sides, corners, faces and edges, with the square-vs-rhombus trap from SOF IMO geometry.5 min read →Perimeter for Class 4: walking around the edge of a shapeWhat perimeter means, the rectangle and square formulas Class 4 children need, worked examples, and the perimeter-vs-area trap in SOF IMO papers.5 min read →Class 4 IMO preparation: the year fractions and geometry arriveHow to prepare a Class 4 child for the SOF IMO: large numbers, roman numerals, fractions and geometry — plus a routine that fits a nine-year-old.6 min read →