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
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