Katie Steckles took over the puzzle column at New Scientist a year ago and transformed it into BrainTwisters. To celebrate, she delves into the math behind a puzzle involving a calculator keyboard. By following specific rules, you can create four-digit numbers that are divisible by 11. The article presents the formulae for creating clockwise and anticlockwise rectangles and explains the neat algebraic reasoning behind it. Through rigorous testing, it’s discovered that the alternating sum of digits leads to multiples of 11. Additionally, an interesting observation by Colin shows an alternative pattern to ensure divisibility by 11. The puzzle column promises more math fun, so stay tuned for upcoming challenges.
https://aperiodical.com/2024/12/a-puzzle-about-a-calculator/