Amileage test is conducted for a new car model. thirty randomly selected cars are driven for a month and the mileage is measured for cach. the mean mileage for the sample is 28.6 miles per gallon (mpg) and the sample standard deviation is 2.2 mpg estimate a 95% confidence interval for the mean mpg in the entire population of that car model.

Explanation:

Given : Sample size : n= 30 , it means it is a large sample (n≥ 30), so we use z-test .

Significance level :

Critical value:

Sample mean :

Standard deviation :

The formula to find the confidence interval is given by :-

i.e.

i.e.

Hence, the 95% confidence interval for the mean mpg in the entire population of that car model =

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