Large Sample Confidence Interval for a Population Mean

Practice: Gas prices are getting more and more expensive. The average gas price, from a random sample of 100 gas stations, was $3.50. It is assumed that gas prices have a standard deviation of $0.04. Construct an 80% confidence interval for the true mean gas price in the United States.

Practice: You want to take a trip to Paris. You randomly select 225 flights to Europe and find a mean and standard deviation of $1500 and $900, respectively. Construct a 95% confidence interval for the average price for a trip to Paris.

Practice: You want to purchase one of the new Altimas. You randomly select 400 dealerships across the United States and find an average and standard deviation of $25,000 and $2500. Construct a 94% confidence interval for the true average price for the new Nissan Altima.