You would like to construct a 95% confidence interval to estimate the population mean annual income for people over age 40 in your state. You choose a random sample of such incomes and compute the mean of the sample as 40,402.5 dollars with a standard deviation of 7837.7 dollars. (a) What is the best point estimate, based on the sample, to use for the population mean? |dollars (b) For each of the following sampling scenarios, determine which distribution should be used to calculate the critical value for the 95% confidence interval for the population mean. (In the table, Z refers to a standard normal distribution, and t refers to a t distribution.) Could use Unclear Sampling scenario either Z or t The sample has size 100, and it is from a non-normally distributed population with a known standard deviation of 7556. The sample has size 16, and it is from a population with a distribution about which we know very little. The sample has size 18, and it is from a normally distributed population with an unknown standard deviation.