1. Confidence Intervals and Sample Size
Chapter 7
Confidence Intervals and Sample Size
Section 7-2
Confidence Intervals for the Mean (σ Known or n ≥ 30) and Sample Size

2. Confidence Intervals for the Mean (σ Known or n ≥ 30) and Sample Size

5. Which interval is larger? Explain why.
Section 7-2 Exercise #11
A sample of the reading scores of 35 fifth-graders has a mean of 82. The standard deviation of the sample is 15.
Find the 95% confidence interval of the mean reading scores of all fifth-graders.
Find the 99% confidence interval of the mean reading scores of all fifth-graders.
Which interval is larger? Explain why.

9. Find the 90% confidence interval
Section 7-2 Exercise #13
A study of 40 English composition professors showed that they spent, on average, 12.6 minutes correcting a student’s term paper.
Find the 90% confidence interval
of the mean time for all composition papers when  = 2.5 minutes.
If a professor stated that he
spent, on average, 30 minutes correcting a term paper,
what would be your reaction?

10. Find the 90% confidence interval of the mean time for all composition papers when  = 2.5 minutes.

11. If a professor stated that he spent, on average, 30 minutes correcting a term paper, what would be your reaction?

12. Section 7-2 Exercise #16 29 50 40
109 78 6 52 21 15 7 68 16 48 80 79 44 4 49 3 90 8 9 57 64 33 54 95 47
A random sample of the number of farms (in thousands) in various states is found above. Estimate the mean number of farms per state with 90% confidence.

13. 29 50 40
109 78 6 52 21 15 7 68 16 48 80 79 44 4 49 3 90 8 9 57 64 33 54 95 47

15. s = 2.5 confidence level = 95% maximum error = 1 day
Section 7-2 Exercise #23
s = 2.5
confidence level = 95%
maximum error = 1 day

16. s =
confidence level =
maximum error =

17. Confidence Intervals and Sample Size
Chapter 7
Confidence Intervals and Sample Size
Section 7-3
Confidence Intervals for the Mean (σ Unknown and n < 30)

18. Confidence Intervals for the Mean (σ Unknown and n < 30)

19. Confidence Intervals for the Mean (σ Unknown and n < 30)

23. Section 7-3 Exercise #7

24. 5 33 35 37 24 31 16 45 19 13 18 29 15 39 58
132

25. Section 7-3 Exercise #11
A recent study of 28 employees of XYZ Company showed that the mean of the distance they traveled to work was 14.3 miles. The standard deviation of the sample mean was 2 miles. Find the 95% confidence interval of the true mean.

27. If a manager wanted to be sure that most of his employees would not be late, how much time would he suggest they allow for the commute if the average speed is 30 miles per hour?

28. Section 7-3 Exercise #19
The average yearly income for 28 community college instructors was $56,718. The standard deviation was $650. Find the 95% confidence interval of the
true mean.

30. If a faculty member wishes to see if he or she is being paid below average, what salary value should he or she use?

31. Confidence Intervals and Sample Size
Chapter 7
Confidence Intervals and Sample Size
Section 7-4
Confidence Intervals and Sample Size for Proportions

33. Section 7-4 Exercise #5

35. Section 7-4 Exercise #7
A survey found that out of 200 workers, 168 said they were interrupted three or more times an hour by phone messages, faxes, etc. Find the 90% confidence interval of the population proportion of workers who are interrupted three or more times an hour.

37. Section 7-4 Exercise #9

38. Find the 99% confidence interval of the true proportion.

41. Section 7-4 Exercise #15

44. Confidence Intervals and Sample Size
Chapter 7
Confidence Intervals and Sample Size
Section 7-5
Confidence Intervals for Variances and Standard Deviations

45. Section 7-5 Exercise #5
Find the 90% confidence interval for the variance and standard deviation for the time it takes a customer to place a telephone order with a large catalog company is a sample of 23 telephone orders has a standard deviation of 3.8 minutes. Assume the variable is normally distributed.

47. Section 7-5 Exercise #6
Find the 99% confidence interval for the variance and standard deviation of the weights of 25 one-gallon containers of motor oil if a sample of 14 containers has a variance of Assume the variable is normally distributed.

48. Find the 99% confidence interval for the variance and standard deviation.

49. Section 7-5 Exercise #9
The number of calories in a 1-ounce serving of various kinds of regular cheese is shown. Estimate the population variance and standard deviation with 90% confidence.
110 45
100 95
120
130 80
105 90 70
125
108

51. Confidence Intervals and Sample Size
Chapter 7
Confidence Intervals and Sample Size
Section 7-5
Exercise #11

52. Section 7-5 Exercise #11
A service station advertises that customers will have to wait no more than 30 minutes for an oil change. A sample of 28 oil changes has a standard deviation of 5.2 minutes. Find the 95% confidence interval of the population standard deviation of the time spent waiting for an oil change.