Rounding, significant figures, leading-digit estimates, floor and ceiling values and percentage error

What this note covers

1. Why approximation is a named skill rather than a shortcut
2. Rounding rules, and the one rule that matters most
3. Significant figures: a different question from decimal places
4. Leading-digit approximation and fast mental estimates
5. Floor and ceiling values: when the context, not the arithmetic, decides
6. Interval estimates and judging reasonableness
7. Percentage error: measuring how wrong an approximation is
8. How approximation is marked, and the habits that separate a top-band script

8 sections · 12 key terms & formulas · 6 common mistakes