Question

7. Suppose you are told that a 95% confidence interval for the average price of a gallon of regular

gasoline in your state is from $3.38 to $4.27. Use the fact that the confidence interval for the mean is in the form x − E to x + E to compute the sample mean and the maximal margin of error E. (Round your answers to two decimal places.)

x = $  

E = $

8. Anystate Auto Insurance Company took a random sample of 382 insurance claims paid out during a 1-year period. The average claim paid was $1520. Assume σ = $248.

Find a 0.90 confidence interval for the mean claim payment. (Round your answers to two decimal places.)

lower limit   $ 

upper limit   $ 

Find a 0.99 confidence interval for the mean claim payment. (Round your answers to two decimal places.)

lower limit   $ 

upper limit   $ 

9. Three experiments investigating the relation between need for cognitive closure and persuasion were performed. Part of the study involved administering a “need for closure scale” to a group of students enrolled in an introductory psychology course. The “need for closure scale” has scores ranging from 101 to 201. For the 69 students in the highest quartile of the distribution, the mean score was x = 175.90. Assume a population standard deviation of σ = 7.41. These students were all classified as high on their need for closure. Assume that the 69 students represent a random sample of all students who are classified as high on their need for closure. Find a 95% confidence interval for the population mean score μ on the “need for closure scale” for all students with a high need for closure. (Round your answers to two decimal places.)

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upper limit  

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