MPA Worldwide Market Research found the average age in a random sample of adult moviegoers was 39 (source: commercialalert.org/moviemadem.htm). If the sample size was 1000 and the population standard deviation is 9.5 years,
a. Construct a 90% confidence interval estimate of the mean age of all adult moviegoers.
b. Construct an 80% interval estimate.
c. Suppose sample size was 2000. Show the 90% and the 80% intervals.