Here is a non-ref link:

https://www.amazon.com/dp/0521017076

Maths: A Student's Survival Guide: A Self-Help Workbook for Science and Engineering Students 2nd Edition by Jenny Olive

ISBN-10: 0521017076 ISBN-13: 978-0521017077

This one is great for start. It has many exercises too.

https://www.amazon.com/Maths-Students-Survival-Self-Help-Eng...

You're 20 you've got plenty of time.

Not everyone enjoys being an entrepreneur. If you feel like you're the kind of guy who needs stable employment, consider this: get your GED (this should be simple for someone like yourself), and take the SAT.

Then apply for college, you should be able to live off of loans while you finish and keep freelancing for some extra cash. You can get a computer science degree and be done by the time your 24.

Also if you need a little math help get this book http://www.amazon.com/Maths-Students-Survival-Self-Help-Engi...

Once again, you're only 20, you're smart, you'll be fine. Just remember that anything worth doing is hard--if it wasn't hard, everyone would do it, and it wouldn't be worth doing.

I came back to studying after a 12 year break where I hardly used maths. I bought the Students Survival Guide and found it very useful and easy to dip in to after work:

http://www.amazon.com/Maths-Students-Survival-Self-Help-Engi...

It takes you to the level needed by most Science/Engineering undergraduate courses.

I came back to doing maths after a gap of over a decade. I found the student survival guide very clear and useful. I imagine it would be excellent to someone who is not good at maths.

I read the guide every evening while I was cooking (its not a difficult read) and my maths improved greatly.

http://www.netcomuk.co.uk/~jenolive/ http://www.amazon.com/Maths-Students-Survival-Self-Help-Engi...