Math & Calculator Guides
In-depth guides on the math behind our calculators, formulas, worked examples, and plain-language explanations of concepts that come up every day.
How to Calculate BMI: The Complete Guide with Formula & Examples
Learn the BMI formula for metric and imperial units, understand the WHO weight categories, see worked examples, and discover the key limitations of BMI.
Compound Interest Explained: Formula, Examples & the Rule of 72
Master the compound interest formula A = P(1 + r/n)^(nt), see how compounding frequency affects returns, and learn the Rule of 72 for quick mental estimates.
How to Calculate Standard Deviation: A Step-by-Step Guide
Understand what standard deviation measures, learn the difference between population and sample SD, and follow a complete worked example from raw data to final answer.
Solving Quadratic Equations: Three Methods with Worked Examples
A complete guide to solving quadratic equations by factoring, completing the square, and the quadratic formula, with step-by-step worked examples for each method.
Percentage Calculations Explained: Every Type with Examples
Master every type of percentage calculation: finding X% of a number, what percent X is of Y, percentage increase and decrease, and reverse percentage problems.
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