In 2002, the average duration of incoming telephone calls to a furniture store was 9.4 minutes. The manager wants to perform a test to determine whether this average duration of incoming calls has changed. Twenty calls to the store were randomly selected and the mean duration was 10.2 minutes with standard deviation 4.8 minutes. Assuming that the duration of incoming telephone calls to a furniture store is normally distributed, a) Using a 1% level of significance, test whether the mean duration of incoming calls to the store had changed. b) Construct the 95% confidence interval for the population mean duration of the incoming calls to the furniture store.

MATLAB: An Introduction with Applications
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Author:Amos Gilat
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In 2002, the average duration of incoming telephone calls to a furniture store was 9.4 minutes. The manager 
wants to perform a test to determine whether this average duration of incoming calls has changed. Twenty 
calls to the store were randomly selected and the mean duration was 10.2 minutes with standard deviation 
4.8 minutes. Assuming that the duration of incoming telephone calls to a furniture store is normally 
distributed
,
a) Using a 1% level of significance, test whether the mean duration of incoming calls to the store had 
changed.
b) Construct the 95% confidence interval for the population mean duration of the incoming calls to 
the furniture store.

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