Construct a 90% confidence interval of the population mean age for the college students in Example 5 with the sample size increased to 30 students. Compare your answer with Example 5.
a. Identify n, , σ, and zc, and find E.
b. Find the left and right endpoints of the confidence interval.
c. Interpret the results and compare them with Example 5.
Example 5
A college admissions director wishes to estimate the mean age of all students currently enrolled. In a random sample of 20 students, the mean age is found to be 22.9 years. From past studies, the standard deviation is known to be 1.5 years, and the population is normally distributed. Construct a 90% confidence interval of the population mean age. |

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