Question

Use Minitab or any software of your choice for this problem.

A researcher wishes to find the confidence intervals of the average age of the managers of a nationwide chain store. A SRS of 30 managers is selected and the following data are obtained. The standard deviation from past records is 11 years. Use any software to construct 90% 95%, and 99% confidence interval. Copy and paste the output of this analysis. Identify the margin of errors in your output.

43           52           18           20           25           20           45           43           21           42           32           24       32 19           25           26           44           42           41           41           53           22           25           23           21     27           33           36           47           19

Answer 1

Using Excel

Confidence interval = Mean ± Margin of error

Mean = AVERAGE(E3:E32) = 32.03333, where range(E3 : E32 ) is the data range in excel

Part a)

Margin of error = CONFIDENCE.T(0.10,11.0125,30) = 3.4163

Confidence interval = Mean ± Margin of error

90% confidence interval ( 28.6171 , 35.4496 )

Part b)

Margin of error = CONFIDENCE.T(0.05,11.0125,30) = 4.1121

95% confidence interval ( 27.9212 , 36.1455 )

Part c)

Margin of error = CONFIDENCE.T(0.01,11.0125,30) = 4.1121

99% confidence interval ( 26.4914 , 37.5753 )