Free, downloadable answer keys for the online learning system PLATO are found at PlannedBook.com in printable PDF format. Answer keys are also provided to teachers as part of the instructor files included with paid PLATO course membership.
PlannedBook.com features over 200 answer key files that cover several different course tests. However, each of the PLATO online learning system's 100 semesters of classes involve several tests, and not all are readily available for free download. For ready access to printable answer key files, a paid membership to the coursework is recommended, as the teacher files included with the coursework offer teaching guides and answer keys.