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A random sample of 121 checking accounts at a bank showed an average daily balance of...

A random sample of 121 checking accounts at a bank showed an average daily balance of $280. The standard deviation of the population is known to be $66. Construct a 95% confidence interval estimates for the mean. (Round to two decimal places) [Answer , Answer ] Construct a 99% confidence interval for the mean. (Round to two decimal places) [Answer , Answer ]

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Answer #1

We have given that,          
          
Sample mean =$280  
Population standard deviation=$66
Sample size=121  
          
i) 95% confidence interval
Z critical value=1.96  
          
Confidence interval formula is

          
Lower confidence limit =$268.24
Upper confidence limit =$291.76

ii) 99% confidence interval


Z critical value=2.58  
          
Confidence interval formula is

Lower confidence limit =$264.52
Upper confidence limit =$295.48

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