In a very large high school, the junior class has 800 students, 54% of whom are female. The senior class has 700 students, 49% of whom are female. The student council selects a random sample of 40 juniors and a separate random sample of 35 seniors. Let p1 - p2 be the difference in the sample proportions of females. (a)What is the shape of the sampling distribution of ? Why?

b) What is the mean of the sampling distribution?

c) Calculate and interpret the standard deviation of the sampling distribution.