A random sample of 100 record shops found that the average weekly sale of a particular single was 260 copies, with standard deviation of 96.
a) Compute the 95% confidence interval to estimate the true average sale for all shops.
b) To compile the record chart it is necessary to know the correct average weekly sale to within 1% of its true value. How large a sample size is required?
c) Why is an interval estimate better than a point estimate? What factors determine the width of a confidence interval?