I live in Washington state and I’m pretty certain the sales tax here is 10% (slightly higher than your maximum figure of 9.56%). It’s a pretty well known trick here that you can account for tax just by decimal shifting and adding (ex: 5.29$ without would be 5.29$ + 0.529$ ~= 5.81$ with tax). Is that 9.56% an “in practice” figure that accounts for rounding down? I’m curious where you read it.
While I do agree that math gets much easier with interest, and that it gets more interesting the further you get into it, and that math is inherently beautiful, etc. I feel this argument has to fall flat to people who don’t already agree. It’s the education equivalent of when someone says they couldn’t get into an anime and then the fans tell them ‘oh it gets really good around season 9’. You could be completely correct, as you are here, but it’s utterly unconvincing if you don’t already “know.”
To be fair, I think this is mostly a problem with math curricula. Math classes up through high school and early college seem to focus on well trodden solutions to boring problems, and at some (far too late) point it flips around to being creative solutions to interesting problems. I think this could be fixed eventually, but such is the system we have now.