It is known that Latoya read 15 books that is [tex]\dfrac{3}{7}[/tex] of the library books in the classroom.
If [tex]\dfrac{3}{7}[/tex] of all books form 15 books, then [tex]\dfrac{1}{7}[/tex] of all books form 5 books.
If [tex]\dfrac{1}{7}[/tex] of all books form 5 books, then the number of all books in the library can be calculated as [tex]5\cdot 7=35[/tex].
Answer: 35 books.
