Why Does Modelling Salary Changes Feel So Inconsistent in IB Maths?
Salary modelling is one of the most confusing financial contexts for IB Mathematics: Applications & Interpretation students. Unlike simple interest or fixed investments, salaries change in ways that feel irregular and unpredictable. Raises may be annual, percentage-based, capped, delayed, or combined with bonuses, which makes modelling feel inconsistent.
IB uses salary modelling to test whether students can handle realistic financial complexity, not tidy textbook growth. The difficulty lies in interpretation, not calculation.
Why Salary Growth Is Not a Simple Pattern
Many students expect salaries to follow a clean arithmetic or geometric sequence.
In reality, salaries often involve:
- Percentage raises
- Fixed bonuses
- Thresholds or caps
- Irregular timing
IB expects students to recognise that salary growth is piecewise and conditional, not uniform. Treating it as a single clean sequence often produces unrealistic results.
Why Percentage Raises Cause Confusion
Percentage raises feel similar to compound interest, but the context is different.
Students often forget that:
- Raises apply to the current salary
- Raises may stop after a certain time
- Raises may differ year to year
IB frequently penalises answers where students apply a constant growth factor without checking whether the raise structure actually remains consistent.
Why Bonuses and Caps Break Simple Models
Bonuses and salary caps disrupt sequence-based thinking.
A fixed bonus does not compound, while a percentage raise does. Salary caps introduce limits that stop growth entirely. IB expects students to adjust their model when conditions change rather than forcing a single formula across all years.
This is why salary questions often feel messy — intentionally so.
Why Students Feel Unsure What the “Right” Model Is
Unlike pure maths, there may be multiple reasonable ways to model salary change.
IB allows flexibility as long as the model is:
- Clearly defined
- Consistent
- Justified
- Interpreted realistically
Students often lose marks not because their model is wrong, but because they fail to explain assumptions clearly.
Why Salary Modelling Appears in AI Maths
Applications & Interpretation focuses on financial literacy and decision-making.
Salary modelling reflects real economic situations students will face. IB uses it to assess whether students can interpret income realistically rather than just apply growth formulas.
Common Student Mistakes
Students frequently:
- Assume constant growth when it isn’t stated
- Mix fixed increases with percentage increases incorrectly
- Ignore caps or conditions
- Fail to justify assumptions
- Skip interpretation of results
Most mistakes come from oversimplification.
How IB Expects You to Handle Salary Models
IB expects students to:
- Read conditions carefully
- Define how salary changes each year
- Adjust models when rules change
- Justify assumptions explicitly
- Interpret financial outcomes realistically
Marks are often awarded for explanation, not complexity.
Exam Tips for Salary Modelling Questions
Write down assumptions clearly. Identify whether increases are fixed or percentage-based. Check if conditions change over time. Use cautious language in interpretation. IB rewards clarity and realism over neat formulas.
Frequently Asked Questions
Is there always one correct salary model?
No. IB often allows multiple reasonable models. What matters is justification and consistency.
Should I always use a geometric model for salaries?
Only if raises are percentage-based and consistent. IB expects you to adjust when conditions change.
Can I lose marks even if my numbers are right?
Yes. Without clear explanation and assumptions, answers are often incomplete. IB assesses reasoning, not just results.
RevisionDojo Call to Action
Salary modelling feels inconsistent because real finances are inconsistent. RevisionDojo helps IB Applications & Interpretation students build realistic salary models, justify assumptions, and explain outcomes clearly — exactly what examiners reward. If salary questions feel unpredictable, RevisionDojo is the best place to build confident modelling judgement.
