Knowledge Organiser: Rounding and Estimation
Part of Rounding & Estimation · GCSE GCSE Mathematics revision
This topic summary covers Knowledge Organiser: Rounding and Estimation within Rounding & Estimation for GCSE Mathematics. Revise Rounding & Estimation in Number for GCSE Mathematics with 13 exam-style questions and 6 flashcards. This topic appears regularly enough that it should still be part of a steady revision cycle. It is section 6 of 6 in this topic. Use this topic summary to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 6 of 6
Practice
13 questions
Recall
6 flashcards
Knowledge Organiser: Rounding and Estimation
Key Terms
- Decimal places (d.p.): Number of digits after the decimal point
- Significant figures (s.f.): Meaningful digits starting from the first non-zero digit
- Estimation: Finding an approximate answer, usually rounding to 1 s.f.
- Truncation: Cutting digits off without rounding (different from rounding)
Must-Know Facts
- Look at the NEXT digit: 0–4 round down; 5–9 round up
- Leading zeros are NOT significant (0.0045 has 2 s.f.)
- Zeros between non-zero digits ARE significant (101 has 3 s.f.)
- Trailing zeros after a decimal point ARE significant (3.50 has 3 s.f.)
- For estimation: round everything to 1 s.f. first, then calculate
- 3.847 to 1 d.p. = 3.8; to 2 d.p. = 3.85; to 1 s.f. = 4
Key Methods
- Rounding to n d.p.: look at digit in position (n+1); round up if ≥ 5
- Rounding to n s.f.: start counting from first non-zero digit
- Estimation: round each value to 1 s.f., perform simplified calculation
- 0.005372 to 2 s.f. = 0.0054 (first two s.f. are 5 and 3)
Common Mistakes
- Counting leading zeros as significant: In 0.0045, the zeros are placeholders — only the 4 and 5 are significant (2 s.f.)
- Rounding in the wrong direction: Look at the digit after the one you are rounding — if it is 5 or more, round up; if it is 4 or less, round down
- Losing trailing zeros: 3.50 rounded to 2 s.f. keeps the zero — 3.5 has only 2 s.f. but 3.50 shows 3 s.f. of precision
- Estimation: not rounding to 1 s.f.: Round every value to 1 s.f. before estimating — rounding to 2 d.p. makes the calculation just as hard
Revise this topic interactively on PrepWise — self-test mode, tap-to-reveal definitions, and Common Mistakes from examiners.
Try the interactive Knowledge Organiser — free →Keep building this topic
Read this section alongside the surrounding pages in Rounding & Estimation. That gives you the full topic sequence instead of a single isolated revision point.
Practice Questions for Rounding & Estimation
Round 4.673 to 1 decimal place.
A student says '3.50 and 3.5 are exactly the same number so they have the same number of significant figures.' Explain why the student is wrong.
Quick Recall Flashcards
13 questions on Rounding & Estimation — practise free
Instant marking, adaptive difficulty, and 6 spaced repetition flashcards. Free until your GCSEs.
Try PrepWise Free