You are given the sample mean and the population standard deviation. Use this information to construct the 90% and 95% confidence intervals for the population mean. Interpret the results and compare the widths of the confidence intervals.

From a random sample of

38

business days, the mean closing price of a certain stock was

$119.76.

Assume the population standard deviation is

$10.30.

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Part 1

The 90% confidence interval is

(enter your response here,enter your response here).

(Round to two decimal places as needed.)

Part 2

The 95% confidence interval is

(enter your response here,enter your response here).

(Round to two decimal places as needed.)

Part 3

Which interval is wider? Choose the correct answer below.

The 95% confidence interval

The 90% confidence interval

Part 4

Interpret the results.

A.

You can be 90% confident that the population mean price of the stock is outside the bounds of the 90% confidence interval, and 95% confident for the 95% interval.

B.

You can be certain that the population mean price of the stock is either between the lower bounds of the 90% and 95% confidence intervals or the upper bounds of the 90% and 95% confidence intervals.

C.

You can be 90% confident that the population mean price of the stock is between the bounds of the 90% confidence interval, and 95% confident for the 95% interval.

D.

You can be certain that the closing price of the stock was within the 90% confidence interval for approximately

34

of the

38

days, and was within the 95% confidence interval for approximately

36

of the

38

days.