A typewritten or word processed page as for a class essay that is in 12 font, say Times New Roman, and is double spaced and is not the first page bearing identification and title below a header is generally calculated as containing 250 words. A typeset page in a standard book is generally calculated as containing 450 to 500 words. Of course, the word count in typeset books pages can vary widely depending on the publishers printing aims.
The only way to know for sure if you are asking about a page in a book or text book is to make a general estimated count for yourself. Pick one full page width sentence and count the number of words in that sentence. Then count the number of lines on a typical looking page. Next multiply the two numbers together: multiply the number of words in a sentence by the number of lines on the page. This will derive an estimated number of words per page.
I suppose the answer to this question would all depend upon several things--most importantly, the size of the page and the size of the print. A normal sized paperback book will obviously have fewer words than a larger book, assuming the pica size of the print is the same. Of course, if the print size is bigger on the large book, the number of words could actually be smaller in number. The space between lines is also flexible; some print material is much tighter (less space) than others. Most lettering is around 8 pica in size. Some print material is smaller, such as the small agate size used for statistics in the sports section (usually 6 pica). The paperback book I currently have in hand (Lois Lowry's The Giver) has approximately 300-320 words per page. It has 31 lines per page and averages about 10-12 words per line. An older copy of To Kill a Mockingbird has much tighter spacing: The same size paperback as The Giver, it has 40 lines per page and averages about the same number of words (about 400-450 words per page). A larger book with small print, such as an old encyclopedia, may have more than 1000 words per page.
(Sorry, but I don't have a copy of The Watson Go to Birmingham available.)