There are 100 books in the library. there are non-fiction and fiction books. write the fraction of the books that are fiction.

The complete question in the attached figure

Let
x--------------------- > non-fiction books.------------------ > x=60
y--------------------- > fiction books.
we know that 
x+y=100
y=100-x=100-60=40
the fiction books. are y=40

if 100%----------------------- > 100 books
  X---------------------------- > 40
X=40*100/100=40%

40%-------------- > 40/100=20/50=2/5

the answer is
the fraction of the books that are fiction is (2/5)