Required "background" for the passage of Scanavi?

Question

Mathematics

There were no problems with VishMat in the first year, but even from school there were gaps in mathematics for grades 7-9, especially in geometry. Without this knowledge, you can solve Scanavi (just google unfamiliar topics), but I would like to go through the basics in order to structure all that knowledge. From the answers on the toaster, I singled out the following:
1) Course on stepik.org: Basic preparation course for the OGE in mathematics . But I'm not sure if all the topics are for grades 7-9;
2) V.A. Bitner, A Short Course in School Mathematics. There are many examples, there are exercises, good scans and it is written in a fairly simple language, at least based on the first topics;
3) M.Ya. Vygodsky "Handbook of elementary mathematics". This is a reference book and there are no exercises there, that is, it is suitable only as a reference;
4)Khan Academy . I did not see the structuring of the material, everything is scattered by topic and little is clear.
Which one to choose and why? So far, the following option seems more logical to me: 1 -> 2 -> Scanavi + 3 as a reference. Thus, I will have to close all the gaps, at least I hope so. Why is this and Scanavi in ​​general? For admission, but now is not about that. If someone studied mathematics at Khan Academy, then please explain how to study it. I really don't know what level to choose.

Answer 1

Why not just take textbooks on algebra and geometry for grades 7-9? There are theory and tasks and solutions, if suddenly something goes wrong.
At a conscious age, they are studied very quickly.