At the beginning of the school year, of all students in Ms. Chang's science class answered "Agree" to the statement "Science is fascinating", and answered "Disagree." At the end of the school year, answered "Agree" and answered "Disagree." Altogether, of the students gave a different answer at the beginning and end of the school year. What is the difference between the maximum and the minimum possible values of ?
20
40
60
80
100