Everyday Maths
The mental arithmetic that saves you money in a shop, a showroom or a meeting.
A fair coin has no memory, so each flip is still 50/50 no matter what came before — but a run of several flips in a row is a different, much rarer question, and here's the exact arithmetic.
Fair means every item has the same 1-in-N chance — here's how to check that arithmetic yourself, and the real odds behind picking the same thing twice in a row.
UPPERCASE, snake_case, kebab-case, camelCase and the rest are all the same two steps — split into words, then rejoin with different punctuation and capitalization.
Speech is roughly 130–170 words per minute, so dividing a word count by a speaking rate gives an honest estimate before you hit play.
No calendar app needed — subtracting serial day numbers (or adding up the days left in each month) gets you the same answer as a countdown timer.
Word count, character count and the 200-words-per-minute reading-time estimate are three small counts and one division — here's how to do all of it without pasting anything into a tool.
Add 280 days to the first day of the last period and you have the standard estimate — here's the arithmetic, a worked example, and why only about 1 in 20 babies actually arrive on that exact day.
Wider spacing, one sentence per line, cautious syllable marks — a look at what a decoding-focused reformat actually does to a page of text, and what it deliberately leaves alone.
"After I brush my teeth, I'll stretch, read and journal" only works if the minutes actually fit — here's the arithmetic for splitting a time budget evenly, remainder and all.
Gym three times, study twice, laundry once a week — working out which days get what, and which day ends up with nothing, is arithmetic you can do with a week's grid and a pencil.
"45 days from now" and "60 days before the 20th" are the same calculation in opposite directions — here's the method, plus the one habit (forgetting leap days) that throws it off.
A timesheet is just a subtraction with a break taken out — except when the shift crosses midnight, which is where most hand calculations quietly go wrong.