# Unit 5: Homework Assignment 1 The monthly incomes from a random sample of managers at various department stores is shown below. Monthly Income (\$1000s) 3.0 4.0 6.0 3.0 5.0 5.0 6.0 8.0 Using Excel Tem

Unit 5: Homework Assignment 1

The monthly incomes from a random sample of managers at various department stores is shown below.

Monthly Income (\$1000s)

3.0

4.0

6.0

3.0

5.0

5.0

6.0

8.0

Using Excel Template 4 (available in Canvas), compute a 90% confidence interval for the mean of the population. The population of all manager’s incomes is known to be normally distributed. Give your answer in dollars

Unit 5: Homework Assignment 2

The manager of Hudson Auto Repair wants to advertise one price for an engine tune-up, with parts included. Before he decides the price to advertise, he needs a good estimate of the average cost of tune-up parts. A sample of 20 customer invoices for tune-ups has been selected and the costs of parts, rounded to the nearest dollar, are listed below.

91

78

93

57

75

52

99

80

105

62

104

74

62

68

97

73

77

65

80

109

Using Excel Template 4 (available in Canvas), provide a 90% confidence interval estimate of the mean cost of parts per tune-up for all of the tune-ups performed at Hudson Auto Repair.

Unit 5: Homework Assignment 3

The standard deviation for the lifetimes of washing machines is estimated to be 800 hours. What sample size must be selected in order to be 97% confident that the margin of error will not exceed 50 hours?

Unit 5: Homework Assignment 4

The makers of a soft drink want to identify the average age of its consumers. A sample of 16 consumers is selected. The average age in the sample was 22.5 years with a standard deviation of 5 years. Assume the population of consumer ages is normally distributed.

a.

Construct a 95% confidence interval for the average age of all the consumers.

b.

Construct an 80% confidence interval for the average age of all the consumers.

c.

Discuss why the 95% and 80% confidence intervals are different.