Percentage Change: Common Mistakes and Quick Checks
How to avoid common percentage errors in discounts, increases, comparisons and ratios.
Guide topic
Maths Calculator Guides
Guides for percentages, ratios, fractions, area, volume, averages, probability and everyday maths checks.
Small maths mistakes can change a budget, material order, grade estimate or report. The safest approach is usually to slow the calculation down and make the base value clear.
This section covers the everyday formulas people reach for most often, with examples that show where the answer can go wrong.
Maths articles
Guides in this topic
Common maths guides for checking formulas, avoiding mistakes and understanding the working. Start here, then move through the numbered pages when the topic continues.
Standard Deviation and Probability in Plain English
A practical explanation of spread, variation and probability for everyday data checks.
Area and Volume Calculations for Materials
How to move from measurements to paint, tiles, concrete and other material estimates.
Fractions, Ratios and Percentages: How They Connect
A practical guide to moving between fractions, ratios and percentages without losing the base value.
GPA, Credits and Weighted Averages
How GPA uses credits, why weighted averages matter and where school policies can change the result.