The OU maths books are indeed very good. This is the way to go.

I'm studying the Q31 (BSc Maths) on Open University.

I can second this recommendation. The maths books are _excellent_.

It's hard to explain how, but let me try: most of the maths textbooks I possess (plenty of them) are written with the assumption that you attend lectures at a classroom and use them for extra material/exercises/reference.

The OU books are written with the assumption that you learn from them as the primary material, so they go a lot further with regard to explaining things as well as producing them from first principles.

I just skimmed through MU123. The content and level is somewhere around the level of these two courses on Math Academy:

- 5th grade math

- prealgebra

The book does look high quality. But I'm surprised it covers these fundamentals, given it's for a university course.

Yeah, MU123 is basic (high school) mathematics. The reason for that is that the way the Open University works, they have no formal requirements to join, so they cannot assume that students know even the basic stuff (because they might have left school earlier, or they might be out of formal education for years, or be from a different domain, etc), so the aim of that course is to quickly help you catchup regardless your background.

If you are above this level, you would start with the "intensive start", which skips MU123 (allowing you to pick another module in its place) and then starts with MST124 (precalculus, trigonometry and single-var calculus, roughly), moving you on to MST125 (intro to proofs, number theory, more calculus, linear algebra, etc), in a faster pace.

Yeah I get the part about filling in some missing foundation. But it's the level that surprised me. Some of the MU123 content is covered in 5th grade in the US, i.e. around age 10 or 11.

But I guess there are people who will have forgotten that stuff, if they're not using much math day to day.