Who typically writes the study questions and answers for textbooks?
It is getting increasingly rare for an individual to write an entire textbook cover to cover. More often, it is the work of several writers and editors compiled into a single textbook title.
If the publisher of the book is one of the larger companies that distribute to schools and colleges nationwide, which is usually the case now given how much it costs to publish hardcover editions, often times editors write all of the study questions and answers for each section, so they can integrate it into online support websites and programs that are incentives to schools to purchase sets of them.
Long story short, questions and answers in the review sections of books are usually added on in the editing and publishing process as opposed to by the main section authors.