Money & Finance
How VAT Works: Adding and Removing It, and Sales Tax Compared
To remove 20% VAT you divide by 1.2, not subtract 20%. Follow the formulas, a supply-chain example, and a comparison with sales tax.
Articles, page 2
Plain-English guides to the numbers in everyday life: how a calculation works, where people go wrong, and which tool to reach for.
Money & Finance
Inflation and Purchasing Power: What Your Money Buys Over Time
A rise in prices means each unit of money buys less. Here is how to measure inflation, project future prices and work out the value of cash that sits still.
Everyday Numbers
km/h, mph, m/s and Knots: Speed Unit Conversions Explained
Four speed units, each a distance divided by a time. Learn the exact factors, a handy reference table, quick estimates, and why averaging two speeds directly goes wrong.
Time & Dates
Leap Year Rules Explained: Why 1900 Was Not but 2000 Was
Every fourth year is a leap year, except when it is not. Learn the full three-part rule, the reason behind it and a formula for counting leap years.
Everyday Numbers
Mbps vs MB/s: Why Downloads Look Slower Than Your Plan
A 200 Mbps plan that shows 25 on your screen is not broken. Bits and bytes differ by a factor of eight, and this guide shows how to convert and estimate download times.
Everyday Numbers
MPG vs L/100 km: How to Compare Fuel Economy Fairly
Miles per gallon and liters per 100 kilometers describe the same thing from opposite directions. Here is how to convert between them and why the gap matters.
Math & Statistics
Odds vs Probability: How to Convert Between Them
"1 in 4" and "odds of 1 to 4" are not the same thing. Learn the two conversion formulas and how odds ratios differ from risk ratios.
Math & Statistics
P-Values Explained: What 0.05 Does and Does Not Prove
A p-value is often read as the chance a result is a fluke, which it is not. Here is what it measures, with a worked coin-flip example and the mistakes to avoid.
Math & Statistics
Percent Error Formula: How to Calculate It With Examples
Percent error tells you how far a measurement is from the accepted value, relative to that value. Here is the formula, two worked examples and the usual traps.
Math & Statistics
How to Write Numbers in Scientific Notation, Step by Step
Scientific notation writes any number as a value between 1 and 10 times a power of ten. Here is how to convert, calculate and read calculator output.
Money & Finance
Simple vs Compound Interest: How the Gap Grows
Simple interest grows in a straight line and compound interest curves upward. A side-by-side example shows how small the gap is at first and how large it becomes.
Health & Fitness
Sleep Cycles and Bedtimes: Working Out When to Sleep
Count back from your wake-up time in blocks of about 90 minutes to find a sensible bedtime. Here is the arithmetic, a quick-reference table and what the method cannot promise.
Everyday Numbers
US vs Imperial Gallons, Pints, Cups and Spoons
The US and imperial systems share unit names but not sizes. This guide compares gallons, pints, fluid ounces, cups and spoons so a recipe or label is never off by 20%.
Health & Fitness
What BMI Can and Cannot Tell You About Your Health
Two people can share the same BMI and have very different bodies. Here is what the number was designed for, where it falls short, and what to pair it with.
Everyday Numbers
Why a 1 TB Drive Shows 931 GB: Decimal vs Binary Units
No space is missing from a 1 TB drive that reports 931 GB. Two definitions of the same prefixes are in use, and the gap grows with each step up in size.
Everyday Numbers
Why a Cup of Flour Weighs Less Than a Cup of Sugar
Cups and grams are not interchangeable because ingredients differ in density. Here is how to convert between them, and why weighing beats scooping for baking.
Math & Statistics
Z-Scores Explained: Comparing Values on Different Scales
A z-score re-expresses any value as a number of standard deviations from the mean, which lets you compare results that use different scales.