At the beginning of the school year, $20\%$ of all students in Ms. Smith's art class preferred "Painting", and $80\%$ preferred "Sculpture." At the end of the school year, $90\%$ preferred "Painting" and $10\%$ preferred "Sculpture." Altogether, $x\%$ of the students changed their preference between the beginning and end of the school year. What is the difference between the maximum and the minimum possible values of $x$?