A random sample of 125 items is drawn from a population whose standard deviation is known to be σ = 30. The sample mean is x¯ = 860. 
(a) 
Construct an interval estimate for μ with 95 percent confidence. (Round your answers to 1 decimal place.) 
The 95% confidence interval is from _________ to __________ 
(b) 
Construct an interval estimate for μ with 95 percent confidence, assuming that σ = 60. (Round your answers to 1 decimal place.) 
The 95% confidence interval is from ________ to ____________ 
(c) 
Construct an interval estimate for μ with 95 percent confidence, assuming that σ = 120. (Round your answers to 1 decimal place.) 
The 95% confidence interval is from _________ to ____________ 
(d)  Describe how the confidence interval changes as σ increases. 

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