Question 769334
According to a U.S. Census Bureau survey during 2005-2007, the daily one-way commute time of U.S. workers averages 25 minutes with , we'll assume, a standard deviation of 13 minutes. 

An investigator wishes to determine whether the national average describes the commuter time for all workers in the Chicago area. 

Commute times are obtained for a random sample of 169 workers from this area, and the mean time is found to be 22.5 minutes. 

Test the Null Hypothesis at the .05 level of significance 
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Ho: u = 25
Ha: u # 25
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x-bar = 22.5
z(22.5) = (22.5-25)/[13/sqrt(169)] = -2.5
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p-value = 2*P(z < -2.5) = 2(normalcdf(-100,-2.5) = 0.0124
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Since the p-value is less than 5%, reject Ho
Conclusion: 25 is not the average for all workers in te Chicago area.
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Cheers,
Stan H.