The average capacity usage for iPhone users has been estimated as 400 megabytes per month. Assuming this finding to be based on a simple random sample of 80 iPhone users, with a sample standard deviation of s 5 90 megabytes per month, construct and interpret the 95% confidence interval for the population mean usage per month. Given this confidence interval, would it seem very unusual if another sample of this size were to have a mean of 350.0 megabytes per month? Source: Leslie Cauley,

“IPhone Gulps AT&T Network Capacity,”USA Today, June 17, 2009, p. 1B.