What's the difference between a duplex and a simplex eBook file?

For the courses that contain blank sheets on the back sides of many pages, we offer simplex and duplex eBook file options. (If no option is indicated, it is because there are little to no blank pages in the course.) In a duplex file, all blank pages are included in the eBook. Duplex files are intended for printers that will automatically flip a page to print on the back side of the paper. If you have a simplex printer (one that prints on only one side of the paper), then you might prefer the simplex version of an eBook . In simplex files, all of the blank pages have been removed.