The standard deviation for a population is = 14.8. A sample of 25 observations selected from

Question:

The standard deviation for a population is σ = 14.8. A sample of 25 observations selected from this population gave a mean equal to 143.72. The population is known to have a normal distribution.
a. Make a 99% confidence interval for µ.
b. Construct a 95% confidence interval for µ.
c. Determine a 90% confidence interval for µ.
d. Does the width of the confidence intervals constructed in parts a through c decrease as the confidence level decreases? Explain your answer.