How to find the sample size to estimate population mean.
A state highway department is studying traffic patterns on one of the busiest highways in the state. As part of the study the department needs to estimate the average number of vehicles that pass an intersection each day. An arbitrary sample of 64 days gives us a sample mean of 14,205 cars and a sample standard deviation of 1,010 cars. After computing the confidence interval, the highway department officials that the precision is too low for their needs. They feel the precision must be 300 cars. Given this precision and needing to be 99% confident, how many days do they need to sample?