Math & Science

How age calculators work: the month-day comparison method, leap year rules, the February 29 problem, and how age is counted around the world.

A practical unit conversion guide for length, weight and temperature, with tables, formulas, mental shortcuts, and the errors that cause problems.

Complete guide to area and volume formulas for every common 2D and 3D shape, with worked examples, surface area formulas, and the unit mistakes to avoid.

Five easy methods to calculate percentages, including mental shortcuts, percentage change, reverse percentages, and the mistakes that trip most people up.