Guides
Plain explanations of the methods behind the calculators — the formulas, the worked examples, and the places people usually go wrong. Every guide links to the tool that does the same job for you.
How to Divide FractionsDividing fractions is multiplying by the reciprocal. This guide walks through fraction by fraction, whole numbers both ways, and mixed…Fraction to Decimal ChartA printable fraction to decimal chart for halves through sixteenths, plus how to convert in both directions and how to…How to Calculate Your Final GradeWork out a final grade when assignments carry different weights, convert the result to a letter grade, and find the…How to Calculate a Discount, Sales Tax and a Tip in Your HeadThe mental shortcuts for percentages off, adding sales tax and working out a tip, plus what to do when two…Negative Number RulesThe sign rules for negative numbers, why subtracting a negative adds, and how the number line makes every case obvious.…Rounding to Decimal PlacesHow to round to one or two decimal places, to the nearest hundredth or cent, and why rounding in stages…X Out of Y as a PercentageTurn any score into a percentage: 15 out of 20, 26 out of 30, 20 out of 25 and the…How to Find the AverageThe four averages, the formula for each, and how to pick the right one. Covers why the mean misleads on…