national surveys show that on average, college freshmen spend 7.5 hours a week going to parties. the dean believes that at her college, which has nearly 3,000 freshmen, students are more diligent and spend less time in such frivolous activities. she directs her assistant to take a simple random sample of 100 freshmen and then interview them. the assistant finds that on average, they report 5 hours a week going to parties, and the sd is 9 hours. is the difference between 7.5 and 5 real?