In order to set rates, an insurance company is trying to estimate the number of sick days that full time workers at an auto repair shop take per year. A previous study indicated that the population standard deviation was 2.1 days.
How do I find a sample large enough for the company that wants to be 92% confident that the true mean differs from the sample mean by no more than 1/2 day?
How would I find the sample size necessary using a 96% confidence interval?
This solution finds the sample mean corresponding to two given confidence intervals.