The standard deviation for a population is ? = 15.3. A sample of 36 observations selected from this population gave a mean equal to 74.8. a. Make a 90% confidence interval for ? . b. Construct a 95% confidence interval for ? . c. Determine a 99% confidence interval for ?. d. Does the width of the confidence intervals constructed in parts a through c increase as the confidence level increases? Explain your answer.

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