Formulas
Each formula page states the formula, defines every symbol, works an example and links to a calculator that applies it.
Percentages and numbers
- Percentage Formulapart = percent × whole, and its two rearrangements.
- Percentage Change FormulaChange relative to the original value, for increases and decreases.
- Percentage Difference FormulaRelative difference between two values using their average.
- Average FormulasFormulas for the mean, median, mode, weighted mean and geometric mean.
- Ratio FormulasSimplifying ratios, sharing in a ratio and converting ratios to fractions.
- Proportion FormulaSolving a/b = c/d with cross-multiplication; direct and inverse proportion.
Algebra, probability and motion
- Quadratic Formulax = (−b ± √(b² − 4ac)) ÷ 2a, where it comes from and how to use it.
- Slope Formulam = (y₂ − y₁) ÷ (x₂ − x₁), line equations and grade percentage.
- Probability FormulasBasic probability, complements, and rules for combining events.
- Distance FormulaDistance and midpoint between coordinates in two or three dimensions.
- Speed Formulaspeed = distance ÷ time, with average speed and unit tips.