📅 Math & Dates guides

Why everyday maths trips people up

Most of the arithmetic we need in daily life is simple, but it hides small traps: a 50% rise followed by a 50% fall does not bring you back to where you started, the average of a list can be pulled far away by one unusual value, and "30 days from today" depends on which month you are in. These guides walk through each trap with plain language and worked examples so you can do the sum confidently, by hand or with a calculator.

What this topic covers

• Percentages: what percent one number is of another, percentage increase and decrease, and percentage points versus percent.
• Averages: mean, median and mode, when each one is the fairest summary, and how a weighted average works.
• Dates: exact age in years, months and days, the number of days between two dates, and business days that skip weekends and holidays.

How to check your answer

A good habit is to estimate before you calculate. If a price rises from 80 to 100, the change is 20, which is a quarter of 80, so the answer should be 25%. If your calculator shows 20%, you divided by the wrong number. For dates, count one small case on a calendar first, then trust the tool for the long range. Each article below ends with a short FAQ that covers the edge cases readers ask about most, such as leap years and inclusive counting.