Mathematical Modelling for IB Maths AI & AA
Modelling is the skill of taking a real-world scenario — money, populations, temperature, motion — and translating it into equations you can actually solve. In IB Maths AI it's the whole point; in AA it's a Paper 3 staple. The examiner rewards the set-up at least as much as the number at the end.
Why it matters
- Compound interest, exponential decay and rate-of-change models appear in every single IB Maths past paper since 2019.
- Paper 3 wraps modelling inside a story you've never seen — the marker is checking whether you can spot the right type of relationship before you touch the GDC.
- The IA (Internal Assessment) is essentially a 12-page modelling exercise. Every skill on this page compounds into a better IA mark.
Examiner signals
-
“A model for … is given by …”When you're given the model, the marks are for using it correctly — units, initial conditions, domain. Read every clause of the modelling assumption.
-
“Comment on the validity of your model …”This appears in almost every IA and Paper 3. Look for extrapolation, unrealistic assumptions (e.g. unbounded exponential growth) and mismatched units. Two easy marks for a sensible paragraph.
-
Financial questionsAlways identify: (i) formula (simple, compound, continuous), (ii) unit of time, (iii) whether the rate is nominal or effective. IB loves catching students who forget monthly-vs-annual compounding.
Interactive fluency practice for Mathematical Modelling for IB Maths AI & AA
A dedicated fluency-first practice set for this skill — thoughtful questions, instant feedback, and worked solutions that build understanding rather than reflexes — is queued up next. Drop your email to be the first to know when it goes live (no spam, one email when it's ready).
FAQ
How do I decide which formula to use for a real-world problem?
Ask: is the quantity changing by a fixed amount (linear / arithmetic), a fixed proportion (exponential / geometric), or driven by a rate that depends on the current state (differential equation)? These are the three question types the IB ever asks.
What's the biggest mistake students make in Paper 3 modelling questions?
Skipping the interpretation step. If you compute V ≈ €5634.13 and stop, you lose the last mark. Always add a sentence: “so after 3 years Priya's investment is worth €5634.13”. This is exactly what mark schemes reward.
Can I use a GDC for every modelling question?
In Paper 1 AA — no. In Paper 2 (both courses) and Paper 3 — yes, and you're expected to. But even with a GDC, always show the model you set up. Naked answers score half marks at best.