Explanations you can try right away
Articles on SQL, Excel, HTML & CSS and touch typing. Each one answers a question you run into while learning, with sources you can check yourself and an exercise you do right in your browser.
How to calculate an average in Excel: blanks, zeros, conditions and weighted averagesIt's one function, yet averages go wrong all the time. See how AVERAGE works, what it skips, and how to average without zeros, with a condition or with weights, on real spreadsheets.Excel · · 11 min read
COUNTIF examples: how to count text, numbers, blanks and duplicates in ExcelOne function, two arguments, and it still miscounts more often than you'd think. On a charity shop's sheet you'll see every kind of criterion at work, and you'll type the formula yourself.Excel · · 12 min read
Excel IF function examples: text, AND, OR, nested IF and IFSOne test, two outcomes and a handful of traps. On a swimming pool's members sheet you'll see IF at work, from a simple choice to three categories, and you'll try it yourself right away.Excel · · 12 min read
Excel SUMIF examples: text, dates, wildcards, and what to do when it isn't workingOne function, three arguments and a handful of traps. On a charity shop's real sheet you'll see every kind of criteria at work, and you can try SUMIF yourself right away.Excel · · 11 min read
SQL interview questions for beginners, with answers you can runMost SQL interview tests ask the same handful of questions and set the same traps. Here they are, with the answer, the query and the result on real data, and two you can solve right on this page.SQL · · 13 min read
12 basic Excel formulas everyone should know, with examples you can tryYou don't need hundreds of functions. Twelve formulas and one habit cover most of the work in Excel, and for each one you'll see where it usually goes wrong.Excel · · 13 min read
VLOOKUP vs XLOOKUP vs INDEX MATCH: which lookup should you use?Three ways to look something up in Excel, and each has its own trap. Here's when to pick which, on a bike courier's sheet, and you can try XLOOKUP right on this page.Excel · · 10 min read
How to center a div in CSS: six ways, and when to use eachCentering horizontally is easy enough; vertically is where it goes wrong. Here are the six ways that work today, when to pick each one, and a few food trucks for you to center yourself, right in this page.HTML & CSS · · 10 min read
HTML vs CSS: what's the difference, and how do they work together?Every web page has two layers, what's on it and how it looks. Here's how HTML and CSS split that work, and you'll write your first CSS rule right in this page.HTML & CSS · · 10 min read
What is a good typing speed? The average, by job, and in keystrokesThere's no official standard, but there's solid research. Here's how your speed compares with 168,960 typists, US government job requirements and a Dutch diploma from 1958.Touch typing · · 10 min read
How long does it take to learn touch typing? What the research saysCourse sites like to promise a number of weeks. The research is more modest and more useful. It shows why you get slower first, why people drift back to two fingers, and how to practise so the skill sticks.Touch typing · · 10 min read
Christophe, founder of Lurndo
Christophe builds Lurndo from Belgium, with short, playful exercises for SQL, Excel, HTML & CSS and touch typing that show straight away what your answer does. On this blog, Christophe answers the questions people run into while learning, with sources you can check yourself.