i'm not familiar with chaffey's program, but i do know my math. i can give you a website you can use to do lots of math problems for practice and it's free. you need to have a good understanding of the basic principals of pre-algebra before you try your hand at algebra. pre-algebra and how to work with fractions and ratios should get you through medication calculations.
here are instructions for accessing
http://www.interactmath.com/ . once you are on the site, click the "enter" button. the next page to come up asks you to select an author and textbook title from a drop down menu. there are many titles there. i recommend martin-gay's books (ex: martin-gay: prealgebra: 4e, enhanced - the 4e stands for the 4th edition of the book and you always want to chose the enhanced versions of the software on this site because they are the newest and most updated programs). after choosing your book title, click the "submit" button. at this point, an installation wizard window pops up. you need to install the mathxl player (it's free). you may have to first install an active x driver, but the installation wizard will tell you that. just follow the instructions of the wizard to download what you need. it is all free. once the mathxl player is downloaded and installed, you will be given access to the practice problems for the textbook you chose. [every time you go onto this site, the installation wizard will appear and check to see that you have the proper software installed in order to use the website.] you will first see a page of drop down menus for chapters, sections, and objectives contained within the textbook you chose. by expanding the chapter menu, you can see how the chapters of the book are organized. pick one. the appropriate sections and objectives for that particular chapter will appear as well as a list of exercises that are links to the problems within that chapter. click on an exercise link and you will be taken to that particular problem. it takes a little time to become familiar with using this program. when you go to a problem (exercise) screen you will find active buttons on all sides of the screen that you need to check out and learn what they do for you. buttons at the top allow you to go back and forth between the previous and next math problem so you don't have to keep going back to that first page with all the drop down menus. as you progress through the problems they become more advanced and increase in difficulty. you can ask the program to show you the step-by-step solution for every single problem it presents to you by clicking on a button on the right side of the page that says "help me solve this". a button below it, "view an example", will show you a sample problem of the same type already solved in a step-by-step fashion. you can also print out a step-by-step solution using the "print" button. you have three tries to get the correct response or answer that the program seeks. once either occurs a new button appears at the bottom of the page: "similar exercise". clicking on this button will bring up another problem of the same type exactly like the one you just solved, but with different numbers. all the same buttons on the right side will still work and you can still ask for step-by-step help if you still need it. that is another great feature about this program. buttons on the left help you to enter things like fractions, radicals and powers. play around with them to see how they work. i could not find a help button or a set of instructions to help in using the program, so you are kind of left on your own to play around with the buttons on the left side to figure out how they work for you.
i had the dvds that came with martin-gay's pre-algebra and intermediate algebra textbooks. she is a terrific lecturer. the trick to math is to work problems over and over and over. interact math will let you do that. you can ask the program to give you more of similar types of problems. i used this website for my intermediate algebra and trig classes and it made a big difference in my understanding of the math. if you use the program enough, you'll begin to see the hierarchy of how the math are organized.
please excuse my dear aunt sally. . .we were just talking about that the other day. this is the mnemonic for the order of mathematical operations (parentheses, exponents, multiplication, division, addition, subtraction).