Show your work. 7) A manager of a cafeteria wants to estimate the average time c

Question

Show your work.

7) A manager of a cafeteria wants to estimate the average time customers wait before being served. A random sample of 49 customers has an average waiting time of 8.4 minutes with a standard deviation of 3.5 minutes.

a) With 90% confidence, what can the manager conclude about the possible size of his error in using 8.4 minutes to estimate the true average waiting time?

b) Find a 90% confidence interval for the true average customer waiting time.

c) With 98% confidence, what can the manager conclude about the possible size of his error in using 8.4 minutes to estimate the true average waiting time?

d) Find a 98% confidence interval for the true average customer waiting time.

Explanation / Answer

a. 1. Open Minitab. Go to Stat> Basic statistics> 1-sample z.

2. In the 'one-sample z for mean' dialog box, enter 49, 8.4 and 3.9 corresponding to 'Sample size', 'Mean' and 'Standard deviation' and click 'OPtions' to select 90 in the 'Confidence Iinterval'. Click OK consecutively. The answer is 0.557.

b. (7.484,9.316) [The output is displayed for the earlier steps only].

c. Change 'Confidence interval' to 98. The answer is 0.557.

d. (7.104,9.696)

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