Question

In a simple random sample of 75 working adults in a city in Virginia, the average commute time for these workers was 23.65 minutes. The standard deviation from this sample was 18.50 minutes. A 95 percent confidence interval for the mean commute time for all adult workers in this city is approximately what?

Answer 1

We have given that,          
          
Sample mean =23.65 minutes  
Sample standard deviation =18.5 minutes
Sample size =75  
Level of significance=1-0.95=0.05  
Degree of freedom =74  
          
t critical value is (by using t table)=   1.993
          
Confidence interval formula is

=(19.39,27.91)           
          
          
          
Lower confidence limit=   19.39 minutes  
          
Upper confidence limit=   27.91 minutes.