In a manufacturing process, we are interested in measuring the average length of a certain type of bolt. Based on a preliminary sample of 9 bolts,...

In a manufacturing process, we are interested in measuring the average length of a certain type of bolt. Based on a preliminary sample of 9 bolts, the sample standard deviation is .3 inches. How many bolts should be sampled in order to make us 95% confident that the sample mean bolt length is within .02 inches of the true mean bolt length?