Marcie bought a total of 20 used books and cds during a yard sale for a total of 54.50$. of books cost 1.50$ each and cds 5$ each, how many of each did she buy? 1 define your variables ,- what are you solving for 2 set up equations - using the information given 3 solve the system using your method of choice

Let numbers of books be 'b' and numbers of CDs be 'c'

We can set up two equations:
Equation [1] ⇒ 
Equation [2] ⇒ 

We are solving for the number of books and the number of CDs bought

When we have two equations in terms of two different variables;  and , that we need to solve, then this becomes a simultaneous equation problem. 

First, rearrange Equation [1] to make either  or  the subject:



Then we substitute  into Equation [2]







Now we know the value of  which is , substitute this value into  we have 

Numbers of books = 13
Numbers of CDs = 7