## Archive for Math

I’ve seen several web pages that explain how to calculate vaccine efficacy, but most of them explain it in terms of a formula rather than explaining what the formula means. Here’s the simplest conceptual explanation I’ve seen: a VE of 90% indicates […] a 90% reduction from the number of cases you would expect if […]

I recently had occasion to learn that 108 and 1008 are both divisible by 18. Which led me to wonder whether any integer consisting of 1 followed by some number of 0s followed by 8 is divisible by 18. And in fact it turns out to be, and I came up with two fun proofs […]

Yesterday, I met Jane and John Kostick, the creators of many delightful and amazing and lovely 3D-geometrical art puzzles and structures, mostly in wood and metal. Their website shows a bunch of their work. Their YouTube channel shows videos of the construction and/or use of various pieces. And their Facebook page provides some more photos […]

It turns out that there are 8 factorial minutes in February. And that’s not just a random coincidence; in fact, you can demonstrate that it’s true without performing any multiplication at all, just some easy factoring. February contains four weeks. The number of minutes in four weeks can be expressed as: 4 weeks x 7 […]