Question

# A random sample of 125 items is drawn from a population whose standard deviation is known...

 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. The interval stays the same as σ increases. The interval gets wider as σ increases. The interval gets narrower as σ increases. The interval gets wider as σ decreases.

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