This is actually stuff they should teach in school explicitly instead of some of the other stuff they teach in math. People need to know this sort of thing for making basic life choices for things like mortgages and things like car leases. Otherwise, one ends up at the mercy of slick salesmen.
I once had a car salesman try to explain to me and my wife why a car lease was such a great deal when it was actually terrible. But he could not even tell me how the payments were calculated never mind compare it with any other form of purchase. I tried to explain to him that we could do the assessment ourselves but he simply said it was too complicated for a customer to understand so I should take his word. My guess is that most of his customers bought his pitch which while brutally incorrect sounded very convincing.
I mean, they do pretty explicitly teach that in highschool math.
Certainly they covered it in Math 31 and Math 30-1 AP when I took them over a decade ago, and they're all over the 20-3 stream rubrics anyway.