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Open textbooks improve learning and teaching by insuring that every student has access to the resources needed to succeed in a course from the first day of class. Open textbooks are free or low-cost on the web and modestly priced for downloads, use on eReaders, or in bound format.
From https://sparcopen.org/wp-content/uploads/2016/01/Open-Education-Fact-Sheet_SPARC.11.10.pdf