In a random sample of forty-eight 200-metre swims has a mean time of 3.12 minutes and a standard deviation of 0.09 minutes.
(a) Construct the 89% confidence interval for the population mean time.
(b) If all the other quantities remain the same, how does the indicated change affect the width of the confidence interval?
(i) Increase in the sample size
(ii) Increase in the level of confidence.