Classroom Notes

How to calculate percentages: three formulas and the mental shortcuts

Every percentage question is one of three calculations. Here are the three formulas with a worked example each, the 10% trick for doing them in your head, and the mistakes that make a sale price or a news headline come out wrong.

How to teach long division, with worked examples

The four steps of long division, three fully worked examples, the partial quotients method many schools teach first, and the mistakes that cost the most marks.

How to Get Better at Math as an Adult: A Realistic 60-Day Plan

Most adults who feel bad at math have three or four specific gaps rather than a general weakness. Here is how to find them in 20 minutes and close them over 60 days.

The order of operations, worked out step by step

One rule, several acronyms, and one detail almost everyone gets wrong. Five worked examples from a single multiplication up to nested brackets with an exponent, plus an honest answer to the viral equations.

Mental math tricks you can learn in one sitting

A working set of calculation shortcuts for adults and older students: the rule, a worked example, the mistake it invites, and the drill that makes it automatic.