Florida National University Statistics - A study of 35 professors showed that

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Question 1 A study of 35 professors showed that the average time they spent creating questions was 13.5 minutes per question. The standard deviation of the population is 3.8. Which of the following is the 99% confidence interval for the average number of minutes it takes to create a test question?

Question 2 A student looked up the number of years served by 35 of the more than 100 Supreme Court justices. The average number of years served by those 35 justices was 13.8. If the standard deviation of the entire population is 7.3 years, find the 95% confidence interval for the average number of years served by all Supreme Court justices?

Question 3 A study of peach trees found that the average number of peaches per tree was 725. The standard deviation of the population is 105 peaches per tree. A scientist wishes to find the 90% confidence interval for the mean number of peaches per tree. How many trees does she need to sample to obtain an average accurate to within 18 peaches per tree?

35

56

72

93

Question 4 The value of  used in the figure below is 0.02.

True

False

Question 5 A previous analysis of paper boxes showed that the the standard deviation of their lengths is 13 millimeters. A packer wishes to find the 95% confidence interval for the average length of a box. How many boxes does he need to measure to be accurate within 4 millimeters?

11

58

41

29

Question 6 A study of 55 white mice showed that their average weight was 3.2 ounces. The standard deviation of the population is 0.9 ounces. Which of the following is the 90% confidence interval for the mean weight per white mouse?

Question 7If a population has a standard deviation of 18, what is the minimum number of samples that need to be averaged in order to be 95% confident that the average of the means is within 2 of the true mean?

612

18

312

36

Question 8In a study using 15 samples, and in which the population variance is unknown, the distribution that should be used to calculate confidence intervals is

a standard normal distribution.

a t distribution with 14 degrees of freedom.

a t distribution with 15 degrees of freedom.

a t distribution with 16 degrees of freedom.

Question 9The t-distribution has a variance that is greater than one.

True

False

Question 10 4 PointsThe t-distribution must be used when the sample size is greater than 30 and the variable is normally or approximately normally distributed.

True

False