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Fractions for the Math Olympiad (Classes 4–5)

Fractions in the SOF IMO for Classes 4–5: equivalent fractions, comparing, the “bigger denominator” trap, and two worked olympiad-style examples.

Fractions are where olympiad papers start separating children who follow procedures from children who picture quantities. A school exercise asks you to shade 3/8 of a circle; the IMO asks whether 3/8 of a pizza is more or less than 2/5 of the same pizza — and offers options built from every plausible wrong comparison.

For Classes 4–5, the paper leans on two ideas above all: equivalent fractions (the same amount written different ways) and comparing fractions. Get those two genuinely solid and most fraction questions in the Mathematical Reasoning and Everyday Mathematics sections open up.

What your child needs to know

  • What the numerator and denominator each mean — parts taken, parts in the whole.
  • Equivalent fractions: multiplying or dividing top and bottom by the same number keeps the value the same.
  • Reducing a fraction to its simplest form.
  • Comparing fractions: same denominators, same numerators, and the benchmark trick of comparing each to 1/2.
  • Fractions of a quantity: finding 3/4 of 20, or 2/5 of 35.
  • For Class 5: adding and subtracting fractions with the same and different denominators.

The traps olympiad setters use

  • The bigger-denominator trap: 1/8 looks bigger than 1/4 to a child who compares denominators like whole numbers. More pieces means smaller pieces.
  • Same numerator, different denominator: 3/5 vs 3/8 — many children call these equal because the tops match.
  • Half-checked equivalence: thinking 4/9 is equivalent to 2/3 because 2 × 2 = 4, without checking that 3 × 2 = 6, not 9.
  • The unequal-parts picture: a shape cut into pieces of different sizes, where counting shaded pieces gives the wrong fraction.

✏️ Try it: equivalent fractions (Class 4 level)

Which of these fractions is equivalent to 2/3?

  1. A4/9
  2. B6/9
  3. C3/4
  4. D2/6
Show the answer

Answer: 6/9. Multiply the top and bottom of 2/3 by the same number, 3: (2 × 3)/(3 × 3) = 6/9. The trap option is 4/9 — the numerator was doubled but the denominator was tripled, so the value changed. And 2/6 is actually equivalent to 1/3, not 2/3.

✏️ Try it: comparing with a benchmark (Class 4–5 level)

Which of these fractions is greater than 1/2?

  1. A3/8
  2. B2/5
  3. C5/8
  4. D4/9
Show the answer

Answer: 5/8. Compare each to half its denominator. Half of 8 is 4, so 3/8 is less than 1/2 but 5/8 is more. Half of 5 is 2.5, so 2/5 is less. Half of 9 is 4.5, so 4/9 is less. Only 5/8 clears the halfway mark. This benchmark trick answers many comparison questions without finding common denominators at all.

In LittleMathematicians, fractions come as game levels for equivalent fractions and comparing, tuned to your child’s mastery so the questions get subtler only when the pictures are truly clear. It is free during early access, and the parent dashboard shows whether it is equivalence or comparison that needs one more round.

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

Equivalent fractions in Class 4: different names, same amountWhy 1/2, 2/4 and 3/6 are the same amount — how Class 4 children find equivalent fractions, plus the NOT-equivalent trap from SOF IMO papers.4 min read →Comparing fractions in Class 4: which slice is bigger?How Class 4 children compare fractions — same denominator, same numerator, and unlike fractions — with the bigger-denominator trap from SOF IMO.5 min read →Decimals, factors & multiples for the Class 5 olympiadThe Class 5 Number Sense pair in the SOF IMO: comparing decimals, factors and multiples, the “longer decimal is bigger” trap, and worked examples.7 min read →