http://en.wikibooks.org/wiki/Pre-Algebra
This is a guide for aspies (like me) who have problems understanding arithmetic. Although, there are a few things you ought to try.
Based on what your difficulty is, whether it be Long Division, Multiplication etc. Choose this area to work on.
1. Open the text of the book to your difficulty area.
2. Try to re-word the text so you can understand it better.
(I used MS Notepad for this, you don't need a real piece of paper to do this.)
3. Work out the problem, then write it on a piece of paper and work it out.
4. Do one lesson a day and always use what you learned in your daily life.
This helped me, I hope it will help you as well
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If great minds think alike, does that mean that stupid minds think differently?