You would like to construct a 95% condence 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 40,6375 dollars with a standard deviation of 7498.5 dollars. (a) what is the best point estimate, based on the sample, to use for the population mean? I: 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 3 refers to a t distribution.) Could use Sam lin scenario ' . _ Unclear p g eltherZorr' "he sample has size 105, and it is from a nonnormallyr distributed 0 G O 0 population. "he sample has size 85, and it is from a nonnormallyr distributed population with a known standard deviation of T809. The sample has size 16, and it is from a normally distributed 0 O G 0 population with an unknown standard deviation