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Rounding to a given number of decimal places or significant figures is used in almost every calculation question, and estimating by rounding to 1 significant figure checks that an answer is sensible.
Students make these errors again and again. Knowing them in advance gives you a head start.
Counting leading zeros as significant figures (0.00456 has 3 significant figures, not 5)
Dropping a trailing zero that shows the accuracy (3.098 to 3 significant figures is 3.10)
Rounding an already rounded answer instead of the original value
Insights pulled from Cambridge IGCSE (0580) examiner reports — the exact mistakes candidates make every year.
For time intervals crossing midnight, split into two parts: time until midnight + time after midnight. Remember an hour has 60 minutes, not 100.
Source: CIE 0580 · Feb/March 2024 · Paper 1 · Q5
For compound interest, the rate and the number of periods must MATCH. 0.25% per month over 5 years = 60 monthly periods (not 5). Don't silently convert to annual — apply the rate as given.
Source: CIE 0580 · Feb/March 2023 · Paper 4 · Q1a(iii)
When finding bounds, always give the final answer in the SAME UNITS as the variable in the question. If l is in metres, bounds must be in metres — convert at the end if your working was in cm.
Source: CIE 0580 · May/June 2023 · Paper 1 · Q18
Based on 3of 500+ insights extracted from CIE 0580 examiner reports (2018–2024).
This topic appears in the Cambridge IGCSE past papers. Our AI tutor can help with it on any question.
Useful for this topic:
Decimal arithmetic is essential for real-world problem solving and calculator-based exam questions. Students need fluency with the four operations on decimals, place value understanding, and converting between decimals and other number forms.
Estimation questions test whether students can round numbers sensibly to perform quick mental calculations. Bounds questions require understanding of upper and lower limits arising from measurements rounded to a given degree of accuracy.
Standard form allows students to work with very large and very small numbers efficiently. It appears in science-context questions and is tested on both non-calculator and calculator papers.
Cambridge publishes a free examiner report for each IGCSE maths series, showing where students lost marks. Here is how to use them for targeted revision.
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