A consumer magazine has contracted a simple random sample of 33 owners of a certain model of automat bile and asked each owner how many defects had to be corrected within the first 2 months of ownership. The average number of defect was x-bar = 3.7, with a standard deviation of 1.8 defects.
a. Use the t distribution to construct a 95% confidence interval for  = the average numbers of defects fro this model.
b. Use the z distribution to construct a 95% confidence interval for  = the average number of defects for this model.
c. Given that the population standard deviation is not known, which of these two confidence intervals should be used as the interval estimate for ?
This solution gives the step by step method for computing confidence interval for estimating population mean.