how to set out a right angle with a tape measure — and all 16 primitive triples up to 100
Built as a memo rather than a table: the thing worth hanging it up for reads across the room, with the full reference in smaller type below it.
Three sizes in one archive — from a sheet on the fridge to a poster on the wall.
A primitive triple is three coprime numbers; every other triple is a multiple of one, like 6, 8, 10. Under each triangle: the m and n that give it.
In every Pythagorean triple one leg is divisible by 3, one by 4, and one of the three numbers by 5. Take 20, 21, 29: 21 is divisible by 3, and 20 by both 4 and 5.
So the product of the three numbers of any triple is a multiple of 60. And no larger number has that property: 3 × 4 × 5 = 60.
Why the numbers can be trusted. Every countable number here is computed from data rather than typed in, and the sheet must pass 8 independent checks before it is allowed to build — how many items there are, the order they come in, and the claim in the highlighted box itself. If one fails, there is no file.
the IWF colour code and the plate count: from target weight to each side of the bar, no calculator
why a “yes” from a test that is right 99 times in 100 is wrong more than nine times in ten when one in a thousand has the thing
the first digit of a number: why a one turns up more than six times as often as a nine, and in which sets that is true
how many people it takes for two of them to share a birthday — and the same count for codes and fingerprints