Fuel Economy, SUV ~ The Environmental Protection Agency (EPA) publishes fuel economy values that are known to be good estimates of the fuel economy a typical driver will achieve under average driving conditions. One of the fuel economy values the EPA publishes is a combined estimate, which represents a combination of city driving (55%) and highway driving (45%). A large car rental company has 15 Ford Explorers in their fleet. They collected fuel economy data from these cars and calculated the sample mean to be 22.39 mpg and sample standard deviation as 0.76 mpg. 1. The car rental company is willing to assume that the conditions are met for constructing a confidence interval. Use the collected data to construct a 95% confidence interval for the mean combined fuel economy for Ford Explorers.
2. If the car rental company wants to estimate the mean combined fuel economy at 90% confidence with a margin of error of no more than 0.25 mpg, how large a sample would they need?
3. A competing car rental company decides to construct a 95% confidence interval for the mean combined fuel economy of the Chevy Equinox using the 25 cars in their fleet as a sample. They obtain an interval of (28.92,30.98). Assume that conditions have been met for constructing this interval and indicate whether each of the statements below is or is not an appropriate interpretation of this confidence interval.
A. We can be confident that 95% of Chevy Equinoxes have combined fuel economy between (28.92, 30.98).
B. We can be 95% confident that the true mean combined fuel economy for the Chevy Equinox is between (28.92, 30.98).
C. If the company were able to obtain 100 random samples of 25 Chevy Equinoxes and used each of the samples to construct a 95% confidence interval, we would expect approximately 95% of those intervals to include the true mean combined fuel economy for this car.