In the library

The library at Lenape Elementary School has 2/5 as many fiction books as nonfiction books. There are 56 books in the school library. How many books are fiction books?

Correct answer:

f =  16

Step-by-step explanation:

$$\begin{gathered} f:n=2:5 \\ f+n=56 \\ f=2/5\cdot n \\ f+n=56 \\ 5f-2n=0 \\ f+n=56 \\ Row2-\frac{1}{5}\cdot Row1\to Row2 \\ 5f-2n=0 \\ 1.4n=56 \\ n=\frac{56}{1.4}=40 \\ f=\frac{0+2n}{5}=\frac{0+2\cdot 40}{5}=16 \\ f=16 \\ n=40 \end{gathered}$$

Try another example