Question

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

Answer 1

Answer:

95% Confidence interval:  (111.02,112.98)

Step-by-step explanation:

Average = 112 seconds

Standard Deviation = 9 seconds

n = 324

Confidence interval:

$\mu \pm z_{critical}\frac{\sigma}{\sqrt{n}}$

Putting the values, we get,

$z_{critical}\text{ at}~\alpha_{0.05} = \pm 1.96$

$112 \pm 1.96(\frac{9}{\sqrt{324}} ) = 112 \pm 0.98 = (111.02,112.98)$