The family incomes in a certain city in 1970 had a mean of $14,200 with a standard deviation of $2600. A random sample of 75 families taken in 1975 produced ¯y = $15, 300 (adjusted for inflation).
(a) Assume σ has remained unchanged and test to see whether mean income has changed using a 0.05 level of significance.
(b) Construct a 99% confidence interval on mean family income in 1975.
(c) Construct the power curve for the test in part (a).