Question

A confidence interval, at the 95% confidence level will be used to answer what the mean annual salary of a Ford car owner is. Data was collected from 34 Ford car owners across the country. the mean annual salary of the 34 Ford owners was 225000. The standard deviation of all Ford owners is known to be $970.

a. The value at the center of the confidence interval represents what? (sample mean, standard dev., population mean, or sample size)

b. is z or t used when building the confidence interval?

c. determine the value of the letter indicated in part b?

d. What is the lower and upper bounds of the confidence interval?

d. if the sample size is decreased by 19 Ford owners, what would happen to the confidence interval? (narrows, widens, or stays the same).

Answer #1

a) Population mean.

b) z is used when building the confidence interval.

c) At 95% confidence level, the critical value is
z_{0.025} = 1.96

d) The 95% confidence interval is

Lower bound = 224673.947

Upper bound = 225326.053

e) The confidence interval would narrows.

As the sample size decreases, the margin of error also decreases. So that the width of the confidence interval becomes narrower.

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