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Author Question: In using the standard normal distribution to construct a confidence interval for the population ... (Read 109 times)

cagreen833

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on: Jun 24, 2018
In using the standard normal distribution to construct a confidence interval for the population mean, what assumptions are necessary if the sample size n is less than 30?

Question 2

A city-paid consumer advocate wants to secure information about the mean length, , of coin-separated car wash cycles. A previous study reported the standard deviation of the length of car wash cycles to be 6 minutes. The advocate timed the wash cycle at 81 randomly selected car wash locations and the mean of the sample was 4.8 minutes. The 90 percent confidence interval estimate is 3.70 to 5.90 minutes. Interpret this interval.


emily12345

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Reply #1 on: Jun 24, 2018
Answer to Question 1

In this case, we need to assume that the population is normally distributed and the population standard deviation  is known.

Answer to Question 2

We have 90 confidence that the population mean is included in this interval.


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