2. The more supplementary content, the worse the effect. The more courses there are, the more make-up teachers tend to skim the surface, only talk about skeleton, not muscle, dry concepts, theorem definition formulas, several kinds of problems and so on. And your math scores won't be much improved.
3. If you seriously make up the math class for half a year, the first half or the second half will start from the place with the worst foundation, and the effect should be good. This requires one-on-one remedial classes. If you are mixed in a big gang, it will not work, and the effect is not great.