If you don't have access to a duplex printer, you can still assemble your purchased PrepTests in a way which mimics the layout of actual book copies. Group the pages in the following pairs, with the blank sides of the two pages back to back: cover and page 2, page 3 and page 4, page 5 and page 6, etc. You can then stack the page pairs and staple through the stack on the left side close to where the spine would be on a book.