Functions
MYP Year 4 Mathematics — Functions
Every functions question this year is secretly testing the same three instincts: is this actually a function, what's allowed in and out of it, and what happens when you stretch, shift or chain it together. The exam bank leans hard on real data — phone bills, bike rentals, reservoirs — because examiners want to see whether you can translate a messy table into notation, not just manipulate an equation someone already gave you.
Overview
A function is the maths department's promise of predictability: feed the same input in twice, you get the same output twice, every time. Composition, transformations, domain restrictions — all of it is just asking one question in different costumes: does this rule behave itself?
- Functions are reliable machines — one input, one guaranteed output.
- Graphs are pictures of rules; transformations are edits made to that picture.
- Domain and range are the machine's operating limits — what it will accept, and what it can possibly spit out.
- Real contexts (cost, growth, rentals) are the whole point — MYP5 exam questions almost always dress functions up as a scenario, not a bare equation.
The shape of the chapter
Command terms this topic loves
| Command term | What it demands | AO | Mark-earning move |
|---|---|---|---|
| State | Give a short answer with no justification required. | AO1 | One correct fact/value earns the mark — extra explanation isn't rewarded but isn't penalised either. |
| Justify | Support a conclusion with a specific reason or test. | AO2 | The mark sits on the REASON (e.g. 'input 2 gives two different outputs'), not just the yes/no answer. |
| Evaluate | Substitute given value(s) and compute a numeric result. | AO1 | Marks awarded for correct substitution AND correct arithmetic — one wrong step loses both. |
| Deduce | Use given information to reach an equation or conclusion, showing the reasoning chain. | AO2 | A correct final rule with no visible working (e.g. gradient, then intercept) rarely gets full marks. |
| Analyse | Break down data to identify a pattern or relationship. | AO2 | Must name the pattern explicitly (e.g. 'constant difference of 2'), not just describe the numbers. |
| Explain | Give reasoning that shows understanding of why something is true. | AO2 | Needs a mechanism, not a restatement — e.g. link back to the vertical line test by name. |
| Advise | Give a reasoned recommendation for a course of action. | AO3 | The numeric answer alone isn't enough — it must be translated into an actual recommendation in context. |
Key point
Overview