Suppose the number of fiction books is 2/7 times the number of nonfiction books. what would be the ratio of the numbers of nonfiction books to the total number of books.

Well, the total amount of books is all fiction books and nonfiction books, let's say is "x", total

now, the fiction books are 2:7 or 2/7 to nonfiction

so, if we divide the total "x" by 2+7, or 9, 2 of those quotients go to fiction and 7 of those go to nonfiction

if we divide "x" by 9, a "whole" is 9/9 or (9/9)x or 1x or just "x"

and we know 7 of those 9ths belong to nonfiction, thus