As others have said, it depends on the book. If we're talking about average science and history books, I can comfortably read 50 pages in an hour. I can read ~20 pages of a science textbook in an hour, including time to highlight and annotate. With fiction, it's more like 80 pages in an hour, but it depends on the author's style and how engaged I am with the plot. In high school, I read Jane Eyre in two days and Atlas Shrugged in about two weeks. I don't usually speed through books, though, especially with nonfiction. Last semester, I spent like a month inching my way through Something Deeply Hidden, which is a book on quantum mechanics. If I'm unfamiliar with a subject, it takes me a long time to get the hang of it.
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I have not the kind affections of a pigeon. - Ralph Waldo Emerson