Rounding lengths without wrecking the next step
Keep full calculator precision mid-working; round only in the final line as instructed.
Key formulas
Early rounding error
Rounding √2 to 1.4 too soon can shift a later angle by a degree — enough to miss a mark.
Follow the paper
“3 significant figures” or “2 decimal places” applies to the presented answer, not to every intermediate.
Exact first
If an exact value is possible (√3, π), prefer it until the question forces a decimal.
Worked example
Worked example
Problem. A calculation gives √2 × 5 = 7.071067… The paper asks for 3 significant figures. What should you write?
Solution. Keep √2 unrounded mid-working. Final answer: 7.07 (3 s.f.).
sf vs dp
3.1416 to 3 s.f. is 3.14; to 3 d.p. is 3.142.
Review quiz
0.08956 to 3 significant figures is:
Practice questions
- Round 0.08956 to 3 s.f.
- Explain one risk of rounding a length before finding an area.
Study notes
Should I write the unrounded value too?
Showing a more precise value then the rounded answer is good practice.