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Formula Library

Searchable knowledge base of formulas — each with its own page, linked tools, and related formulas.

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General (9)

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Percentage proportionamount = (percent / 100) × wholeRelate a percent, a whole, and an amount — solve for any one when two are known.Math
Percent errorpercent error = |observed − true| / |true| × 100%Measure how far an observed value is from a known true value, as a percentage.Math
Ratio and proportionA:B = C:D → A×D = B×CTwo ratios are equivalent when their cross-products are equal.Math
Roundinground(value × 10^p) / 10^p · or nearest k/nReplace a number with a nearby simpler approximation.Math
Exponentiationbase^exponent = resultRelate a base, an exponent, and a power — fill any two to solve for the third.Math
Nth rootⁿ√a = b ⇔ bⁿ = aFind b such that b raised to n equals a.Math
Fraction arithmetica/b ± × ÷ c/d → reduced formOperate on fractions and reduce the result to lowest terms.Math
Long divisiondividend = quotient × divisor + remainderDivide integers with a quotient and remainder (or decimal expansion).Math
Order of operations (PEMDAS)PEMDAS: ( ) then × ÷ then + −Evaluate expressions in standard operator precedence.Math

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