In 2015, the average duration of long-distance telephone calls from a certain town was 3.9 minutes. A telephone company wants to perform a test to determine whether this average duration of long- distance calls has changed. Fifty calls, originating from the town, was randomly selected and the following summary minutes. ∑ ? = 205                  ∑(? − ?̅)2  = 56.43 Calculate the sample mean, ?̅. Calculate the sample standard deviation.

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In 2015, the average duration of long-distance telephone calls from a certain town was 3.9 minutes. A telephone company wants to perform a test to determine whether this average duration of long- distance calls has changed. Fifty calls, originating from the town, was randomly selected and the following summary minutes.

∑ ? = 205                  ∑(? − ?̅)2  = 56.43

  • Calculate the sample mean, ?̅.
  • Calculate the sample standard deviation.
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