These three courses cover secondary (middle/junior high and senior high) school in the system of education used in the U.S., starting with 7th or 8th grade (although middle schools usually start with 6th grade) and going through 12th grade (also known as senior year). The courses spread between the three courses cover the areas of Algebra 1 and 2, Statistics, Geometry, Trigonometry, and possibly Pre-Calculus, but they don't cover any part of Calculus itself. The only part of any of these three courses that may reach down into the U.S. elementary school curriculum (and certainly not down as far as 3rd grade) is the first playlist in Mathematics I, Algebra foundations.

I think that you could build a decent foundation of high school level math by going through the three courses in sequence. If Algebra foundations is too simple for you, just go on to the next playlist, which starts to get into Algebra itself. If you find any of it too difficult fo you, then try some earlier courses, such as 6th, 7th, or 8th Grade Math, Pre-algebra, Algebra Basics. or Basic Geometry.

Once you are done with these three courses, you can try Calculus.

Good luck in your studies!

Many thanks for such a meaningful answer, very kind of you! I have no questions left.

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