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Part I. Confidence Interval When ? is known.

1. Noise levels at various area urban hospitals were measured in decibels. The mean of the noise levels in 84 corridors was 61.2 decibels, and the standard deviation of the population was 7.9. Find the 95% confidence interval of the true mean.

2.The growing seasons for a random sample of 35 U.S. cities were recorded, yielding a sample mean of 190.7 days and the population standard deviation of 54.2 days. Estimate the true mean population of the growing season with 95% confidence.

3.A recent study showed that the modern working person experiences an average of 2.1 hours per day of distractions (phone calls, e-mails, impromptu visits, etc.). A random sample of 50 workers for a large corporation found that these workers were distracted an average of 1.8 hours per day and the population standard deviation was 20 minutes. Estimate the true mean population distraction time with 90% confidence.

4.A study of 415 kindergarten students showed that they have seen on average 5000 hours of television. If the sample standard deviation of the population is 900, find the 95% confidence level of the mean for all students. If a parent claimed that his children watched 4000 hours, would the claim be believable?

5.First-semester GPAs for a random selection of freshmen at a large university are shown below. Estimate the true mean GPA of the freshman class with 99% confidence. Assume ? = 0.62.

PLEASE SEE THE ATTACHED PHOTO NAME STAT 1 . THANKS.

1.9 3.2 2.0 2.9 2.7 3.3 2.8 3.0 3.8 2.7 2.0 1.9 2.5 2.7 2.8 3.2 3.0 3.8 3.1 2.7 3.5 3.8 3.9 2.7 2.0 2.8 1.9 4.0 2.2 2.8 2.1 2.4 3.0 3.4 2.9 2.1