###Human: Shelby had $20 to take to the book fair. She bought one book for $8 and another for $4. She decided to buy as many $4 posters as she could with the money she had left. How many posters can she buy?, ### Assistant: She spent $8 + $4 = $12 on books.
She started with $20, so she has $20 - $12 = $8 left to spend on posters.
Each poster costs $4, so she can buy $8 / $4 = 2 posters. 
 So the answer is :  2