Question

The owner of a retail outlet sold and provided service for copying machines. One type of...

The owner of a retail outlet sold and provided service for copying machines. One type of machine, DW 140 model, needed service often. The owner was interested in the mean time required to service this model and decided not to carry the model if the mean repair time appeared to be more than 40 minutes. The repairman provided the 39 times (in minutes) which is on BlackBoard in SERVICE TIME. IGNORE OUTLIERS

a. b. c.

Construct a 90% confidence interval. Based on the information.
With the given information would the retailer keep this model and why?
If the retailer wanted the margin of error to be plus or minus 2 minutes how many observations from the repairman would she need? Use the sample standard deviation as a proxy for the population standard deviation and keep the same significance level.

23                              

41                              

47                              

27                              

42                              

47                              

28                              

42                              

48                              

33                              

42                              

49                              

35                              

43                              

50                              

37                              

44                              

51                              

39                              

44                              

52                              

39                              

44                              

53                              

39                              

45                              

53                              

39                              

46                              

56                              

40                              

46                              

57                              

40                              

46                              

61                              

41                              

47  

62                              

                              

Homework Answers

Answer #1

Sample size = n = 39

Sample mean = = 44.0513

Standard deviation = s = 8.4572

We have to construct 90% confidence interval.

Formula is

Here E is a margin of error.

Degrees of freedom = n - 1 = 39 - 1 = 38

Level of significance = 0.10

tc = 1.686 ( Using t table)

So confidence interval is ( 44.0513 - 2.2832 , 44.0513 + 2.2832) = > ( 41.7681 , 46.3345)

If the retailer wanted the margin of error to be plus or minus 2 minutes how many observations from the repairman would she need? Use the sample standard deviation as a proxy for the population standard deviation and keep the same significance level.

In this question, we have to find the sample size(n).

Confidence level = 0.90

tc = 1.686

Margin of error = E = 2

Population standard deviation = = 8.4572

We have to find sample size (n)

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