In: Statistics and Probability
You want to estimate the mean weight of quarters in circulation. A sample of 40 quarters has a mean weight of 5.678 grams and a standard deviation of 0.063 gram. Use a single value to estimate the mean weight of all quarters. Also, find the 95% confidence interval for the average weight of all quarters
We have given that,      
   
          
Sample mean =5.678 grams   
Sample standard deviation = 0.063 grams
Sample size =40  
Level of significance=1-0.95=0.05  
Degree of freedom =39  
          
t critical value is (by using t table)=  
2.023  
          
Confidence interval formula is       
   
=(5.6578,5.6982)      
          
          
Lower confidence limit=5.658 grams      
          
Upper confidence limit=   5.698 grams