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: 112.5 seconds

Explanation:

I just took the test

Answer 2

95% Confidence interval: (111.02,112.98)

Explanation:

Average = 112 seconds

Standard Deviation = 9 seconds

n = 324

Confidence interval:

`\mu \pm z_(critical)(\sigma)/(√(n))`

Putting the values, we get,

`z_(critical)\text{ at}~\alpha_(0.05) = \pm 1.96`

`112 \pm 1.96((9)/(√(324)) ) = 112 \pm 0.98 = (111.02,112.98)`