>>13713126I tutored math while at community college and university.
If you say you stopped in 8th grade I will assume you know this much:
>Counting >Addition/Subtraction >Multiplication/Division >Fractions>Decimals>Percents>Areas of boxes (squares, rectangles, triangles)>Areas of circles >Perimeter of boxes >Perimeter of circles >Diameter of circlesIf you don't have this down then go back and learn that in order first. Additionally, for Addition/Subtraction, even if you can work out problems on paper, you should practice doing both for numbers with 3 or fewer digits in your head. Example (3 + 7 =?, 35 - 14=?, 950-42=?)
If you can work out those problems in your head things will be a lot easier for you.
In addition to that, you want to know your Multiplication tables by heart through at least 10 and probably 12. Example (9 x 4=?, 3 x 7 =?, 11 x 11 =?). Just use index cards to drill on this. It is okay to 100% memorize these. Again this will make later topics way easier.
If you have all that done, then you are nearly done for the bare minimum needed to survive. Next are these:
>Basic Algebra>Powers (eg. what is 2 to the 4th power?) >Interest RatesOkay stop. This is enough to survive. If you learn just this well enough to apply it to your everyday life you can:
>Tip whatever % of a check you like. (often in your head)>Split a tab at a bar with friends evenly>Understand how a credit card works >Understand how to factor in repairs, depreciation, and interest for a car loan. >Use Microsoft Excel >Run a small business (some Excel training required)Essentially this is enough to not get swindled by every banker, salesman, and cashier you meet. You will still lose at cards unless that was something you were good at before.
If you need a GED or something then you have to keep going.
>Trigonometry >Advanced Algebra (Algebra II)>Pre-Calculus/Calculus 
