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Suppose that a customer service center claims that the telephone calls it receives last 112 seconds on average, with a standard deviation of 9 second. If you took a sample of 324 telephone calls, which of the following mean times would be within the 95% confidence interval

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Answer:

95% Confidence interval:  (111.02,112.98)

Step-by-step explanation:

Average = 112 seconds

Standard Deviation = 9 seconds

n = 324

Confidence interval:

[tex]\mu \pm z_{critical}\frac{\sigma}{\sqrt{n}}[/tex]

Putting the values, we get,

[tex]z_{critical}\text{ at}~\alpha_{0.05} = \pm 1.96[/tex]

[tex]112 \pm 1.96(\frac{9}{\sqrt{324}} ) = 112 \pm 0.98 = (111.02,112.98)[/tex]

Answer: 112.5 seconds

Step-by-step explanation:

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