In fact, my kids have used my old books to help them with AP Physics in high school. They tell me they like the lower content of distracting color-filled "circus acts" (as they call it) and better explanations.
How much of the math, physics and chemistry has changed? I would guess, depending on stage of learning and subject, somewhere between 0% and 10% (with 10% possibly being an exaggeration). It is nothing less than ridiculous that students have to buy books on Algebra, Trigonometry, Calculus, etc. for $60 or more.
This is the kind of thing that really gets me going about just how badly our system of education has derailed in some areas. Most school books, at a national level, should be freely available and used year over year, preferably in electronic form.
What is wrong with a, let's call it, federally publish set of books covering the sciences and other subjects? They could be evolved over time.
I know these things exist in various forms, we simply don't seem to lay down the law and use them. CK-12 used to be about books, now they seem to have expanded beyond that:
What's wrong with these books?