How to Work Out a Tip Without a Calculator
Tipping is just percentages. Learn the 10% trick, the 20% double, and a clean way to split the bill, then check yourself with a calculator.
Articles, page 7
Plain-English guides to the numbers in everyday life: how a calculation works, where people go wrong, and which tool to reach for.
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.
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.
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.
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.
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.
Mental Shortcuts for Metric and Imperial Conversions
A handful of exact factors and a few easy tricks cover most everyday conversions. See how accurate each shortcut is, and why metric prefixes reduce conversion to moving a decimal point.
Converting Minutes to Decimal Hours for Timesheets and Pay
Pay is calculated in decimal hours, but clocks run in base 60. Learn the conversion, a quick reference table, and why rounding each shift can shave off pay.
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.
Nautical Miles, Fathoms and Leagues: Old Distance Units
Sailors and pilots still measure distance in nautical miles, and old units like fathoms and leagues turn up in books and charts. Here is what each one is and how to convert it.
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.
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.