The 1089 rule (having fun with algebra)
The “1,089 rule” isn’t really a rule at all, it’s more like a fun thing that happens with numbers that you can explain with algebra. What it tells you is that you can pick any 3-digit number with decreasing digits, like 742 or 863, and that if you reverse the digits of that original number, and then subtract the reversed number from the original number, that you’ll get a result from that subtraction. And then if you reverse the digits of that result, and then you add the result together with the reversed result, that you’ll get 1,089 every time, no matter which 3-digit number you started with. Which, when you think about it, is pretty crazy considering that there are a whole lot of 3-digit numbers out there.