Number and Operations
MYP Year 5 Extended Mathematics — Number strand (Number and Operations)
Every question in this strand is really testing one habit: do you know which number is the one that actually matters? The raw measurement, the rounded measurement, or the true value hidden behind both — examiners build entire mark schemes around students picking the wrong one at the justification step. Get comfortable moving between exact values, rounded values, and error bounds, and the rest (fractions, indices, standard form, ratio) is just careful bookkeeping.
Overview
This strand covers how numbers are represented, approximated, and manipulated — and, critically, how much trust you can place in a number once it has been rounded. Roughly half the marks in this strand come from four skills: rounding correctly, quantifying the error a rounding introduces, justifying a decision against a stated threshold, and moving fluently between fractions, decimals, percentages and standard form.
- Financial maths, ratio/proportion and fraction operations are the 'mechanics' — get the procedure right and the mark is yours.
- Error bounds, significant figures and scientific notation are the 'judgement' skills — examiners test whether you know which value (rounded, true, or bound) answers the actual question being asked.
- Justify / Deduce questions almost always hinge on re-reading whether a regulation or threshold applies to the recorded (rounded) figure or the true (unrounded) one.
The shape of the chapter
Command terms that decide your method
| Command term | What it demands | AO | Mark-earning move |
|---|---|---|---|
| Calculate | Obtain a numerical answer showing the relevant working — a bare correct answer with no method shown can lose a working mark if the final answer is wrong. | AO1/AO2 | Write the formula/substitution line even when you could do it mentally. |
| Estimate | Round values sensibly (usually to 1 s.f.) BEFORE calculating, to get a sensible approximate answer — not calculate exactly then round. | AO2 | Show the rounded values used, not just the final approximate answer. |
| Justify | State a conclusion AND give a reasoned argument using a correct numerical comparison — a conclusion with no comparison shown scores 0. | AO3 | Explicitly compare the relevant value (true, rounded, or bound) against the threshold, in words. |
| Deduce | Use given information/pattern to establish a result or formula, showing the logical link, not just stating it. | AO3 | Show at least one intermediate step connecting the given data to the general formula. |
| State | A short answer with no working required — but for rules (e.g. 'state the rounding rule') the full rule in words is needed for the mark. | AO1 | Don't over-explain — but don't under-explain either; match the mark allocation. |
| Compare | Identify similarities AND differences between two things — one-sided answers lose marks. | AO3 | Structure the answer explicitly around both quantities, not just one. |
Key point
Overview