The Badik Construction Company limits its business to constructing decks. The mean time to construct one of its standard decks is 8 hours for a two-person construction crew. The information is based on a sample of 40 decks recently constructed. The standard deviation of the sample was 3 hours.
a. Determine a 90% confidence interval for the population mean.
b. Would it be reasonable to conclude that the population mean is actually 9 hours? Justify your answer