Features:

• It calls itself a “Store,” but they are not a publisher. Open TextBook Store provides freely and openly available math textbooks created by Washington CTC faculty.
• You can either download the whole book for free, or order a printed version which costs below 20 dollars.
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License Setting

• All textbooks on this site are licensed under CC BY 3.0.
• This license lets you distribute, remix, tweak, and build upon the original work, even commercially, as long as you credit the author for the original creation.

Sample Attribution

Estimating with Decimals (p. 250) from  Arithmetic for College Students by David Lippman is licensed under CC BY 3.0.