These Books are permanently free (assuming Amazon’s bot doesn’t fuck up the price again):
Algebra – The Very Basics: If you’re looking for a gentle introduction to basic mathematics, look no further. This book picks you up at the very beginning and guides you through the foundations of algebra using lots of examples and no-nonsense explanations. Each chapter contains well-chosen exercises as well as all the solutions. No prior knowledge is required. Topics include: Exponents, Brackets, Linear Equations and Quadratic Equations. For a more detailed table of contents, use the “Look Inside” feature.
Math Shorts – Derivatives: The rich and exciting field of calculus begins with the study of derivatives. This book is a practical introduction to derivatives, filled with down-to-earth explanations, detailed examples and lots of exercises (solutions included). It takes you from the basic functions all the way to advanced differentiation rules and proofs. Check out the sample for the table of contents and a taste of the action. The series continues with the second installment “Math Shorts – Derivatives II”. Note: Except for the very basics of algebra, no prior knowledge is required to enjoy this book.
Enjoy yer free stuff!