MYP Maths: Significant Figures & Rounding — Frequently Asked Questions

Sig figs trip students up because they mix three ideas — place value, decimal places, and measurement precision — into one rule. Typical mistakes: miscounting zeros, rounding mid-calculation, and ignoring the stated precision. I see the same slip every cohort — a trailing zero dropped when it should count as significant.

Every non-zero digit is significant. Zeros count too, but only when they sit between other digits (205 has three sig figs) or come after a decimal point showing measured precision (3.20 has three sig figs). Leading zeros, like in 0.0034, never count — they only fix the decimal point's position.

Decimal places count digits after the decimal point only; significant figures count all meaningful digits in a number, wherever they fall. Round 0.004521 to 2 decimal places and you get 0.00 — useless. Round it to 2 significant figures and you get 0.0045 — the rule MYP actually wants for accuracy.

Unless told otherwise, use three significant figures for final answers — the standard convention across MYP and DP mark schemes. Always check the command word first: if it says 'to 2 sig figs' or 'nearest whole number,' follow that exactly, even when 3 sig figs feels more natural.

Count from the first non-zero digit to find the required number of significant digits, then check the next digit to decide whether to round up. Example: round 0.048273 to 3 sig figs — the first three digits are 4, 8, 2, and the next digit (7) rounds the 2 up, giving 0.0483.

Round only at the end. Carry full calculator precision through every intermediate step, then apply the required rounding once to your final answer — rounding early compounds error and can push your answer outside the accepted range in the mark scheme.

The single biggest mistake is rounding too early — using an already-rounded intermediate value in the next step, which compounds error and can shift your final answer outside the mark scheme's accepted range. Examiners see this constantly in multi-step area, trigonometry, and compound interest problems.

Yes. The MYP: Mathematics guide expects appropriately accurate final answers across every criterion, and Criteria A and D specifically reward correct use of significant figures and rounding in real-life and abstract problems. In practice, an answer with the wrong precision usually loses one accuracy mark even when the method is fully correct.

Because precision reflects real mathematical and scientific practice — an engineer or scientist reporting more digits than their measurement justifies is presenting false accuracy. The MYP's real-life contexts strand (Criterion D) exists precisely to test whether you understand that a calculator answer isn't automatically a meaningful one.

MYP rounding is mostly about accuracy conventions — usually three sig figs unless stated otherwise. DP Maths AA and AI apply the same three-sig-fig default, but the accuracy penalty is stricter: an unrounded or wrongly-rounded final answer can lose an accuracy mark even in an otherwise fully correct response.

Short, focused practice beats long review sessions — ten mixed rounding questions a week, checked against a full mark scheme, fixes most errors within a term. On RevisionPrep, the MYP Mathematics Topical Worksheets isolate significant figures and rounding as their own practice set, with Revision Notes covering the exact command-term wording examiners use.