1)An assistant principal wants to learn about the opinions of parents on school physicals. She has 2000 students, 20% of whom are freshmen, 30% of whom are sophomores, 20% of whom are juniors and 30% of whom are seniors. She decides to randomly select 50 freshmen, 40 sophomores, 30 juniors and 60 seniors to form a sample of students. What type of sampling is this? ___________________________________

a. Suppose that 10 of the freshmen parents, 5 of the sophomore parents, 15 of the junior parents and 20 of the senior parents were in favor of school physicals, what is the overall proportion of students whose parents are in favor of school physicals? _____________

b. The number obtained in (6a) above is called a ____________, since it was derived from a sample.