Fuel efficiency of manual and automatic cars, Part I. Each year the US Environmental Protection Agency (EPA) releases fuel economy data on cars manufactured in that year. Below are summary statistics on fuel efficiency (in miles/gallon) from random samples of cars with manual and automatic transmissions. Do these data provide strong evidence of a difference between the average fuel efficiency of cars with manual and automatic transmissions in terms of their average city mileage? Assume that conditions for inference are satisfied.22
City MPG
Automatic Manual Mean 16.12 19.85 SD 3.58 4.51 n 26 26
City MPG
automatic manual
15
25
35
Fuel efficiency of manual and automatic cars, Part II. The table provides summary statistics on highway fuel economy of the same 52 cars. Use these statistics to calculate a 98% confidence interval for the difference between average highway mileage of manual and automatic cars, and interpret this interval in the context of the data.23
Hwy MPG
Automatic Manual Mean 22.92 27.88 SD 5.29 5.01 n 26 26
Hwy MPG
automatic manual
15
25
35