MYP Maths: Ratio, Proportion & Rates — What Students Need to Know

MYP 4-5 students need to compare quantities using ratio (e.g. 3:5), solve unknowns using proportion (direct and inverse), and apply rates — speed, density, unit price — to real contexts. According to the MYP: Mathematics guide, these skills sit in the Number and Algebra strands, assessed via Criterion A (Knowing and Understanding) and Criterion D (Applying Mathematics).

A ratio compares two quantities of the same kind — 3 boys : 5 girls. A proportion states that two ratios are equal, used to solve for an unknown, like x/4 = 15/20. A rate compares two different quantities, such as km per hour, so the units in your final answer actually change.

In direct proportion, both quantities rise or fall together at a constant ratio — double one, double the other (y = kx). In inverse proportion, one quantity increases as the other decreases, keeping their product constant (y = k/x). Spotting which applies is the biggest hurdle I see in Criterion A questions.

A rate links two different units — distance/time for speed, mass/volume for density, price/quantity for unit cost — and MYP problems expect correct unit conversion before you divide. Get the units wrong, mixing km with m or seconds with hours, and the whole calculation collapses even if your method was right.

Read the question twice, identify exactly what's being compared, set up an equation using equivalent ratios or the constant of proportionality, solve for the unknown, then check the answer makes sense in context. Examiners marking Criterion A want to see this reasoning written down, not just the final number.

The three I mark most often: writing a ratio the wrong way round (5:3 instead of 3:5), confusing direct with inverse proportion, and forgetting to convert units before dividing in a rate question. All three are avoidable — they're about reading carefully, not needing harder maths.

Show full working, state which type of proportion you're using and why, and finish with a sentence linking your answer back to the real-world context — that's what separates a mid-band response from a top-band (7-8) Criterion D answer. Practising exam-style questions with mark schemes is the fastest way to build this habit.

Mostly Criterion A (Knowing and Understanding) and Criterion D (Applying Mathematics in Real-Life Contexts), though a well-designed investigation can also pull in Criterion B (Investigating Patterns) and Criterion C (Communicating). According to the MYP: Mathematics guide, each criterion is marked out of 8, with strands describing what each achievement level looks like.

Yes — the optional MYP eAssessment for Mathematics provides an on-screen calculator for most questions, but several ratio and proportion items are deliberately designed to test method over computation, so you still need to show reasoning. Schools running their own school-based exams instead usually follow the same command-term structure.

Direct and inverse proportion reappear as functions (y = kx and y = k/x) in both DP Mathematics: Analysis and Approaches and Mathematics: Applications and Interpretation, and rates underpin kinematics and financial maths later on. Students shaky on MYP proportion typically struggle with DP variation and rates-of-change questions in Year 12.

It's an early signal, not a guarantee. Students who find inverse proportion and abstract algebra intuitive tend to settle comfortably into Analysis and Approaches; students who prefer applying the same ideas to real contexts — finance, science, statistics — often thrive more in Applications and Interpretation. Either way, the underlying skill needs to be solid first.

Yes, meaningfully — MYP 4-5 introduces inverse proportion, compound rates and multi-step real-life contexts that go well beyond the simple ratio-sharing problems typical of MYP 1-3. The jump matters because MYP 4-5 achievement levels start feeding into predicted grades and Diploma subject-choice conversations with your coordinator.

Practice with full worked solutions beats generic worksheets, because your child needs to see how examiners expect reasoning to be written, not just the final answer. On RevisionPrep, the MYP Mathematics Topical Worksheets and Revision Notes cover this exact strand, with worked examples mapped against Criteria A and D.

Most students self-study this strand successfully — it's a skills topic built on repetition, not deep conceptual difficulty, so varied practice closes gaps fast. If your child is still confusing direct and inverse proportion after two or three practice sets, that's the moment to add targeted worksheet practice rather than more general revision.