Exhibit 8-4
In order to estimate the average electric usage per month,a sample of 81 houses was selected,and the electric usage was determined.Assume a population standard deviation of 450-kilowatt hours.
-Refer to Exhibit 8-4.If the sample mean is 1,858 KWH,the 95% confidence interval estimate of the population mean is
A)1,760 to 1,956 KWH
B)1,858 to 1,956 KWH
C)1,760 to 1,858 KWH
D)None of these alternatives is correct.

Question

Quizplus · Accepted Answer

The 95% confidence interval is calculated using the formula: sample mean ± (Z * (population standard deviation / sqrt(sample size))). Here, Z for 95% confidence is 1.96. So, 1858 ± (1.96 * (450 / sqrt(81))) gives the interval 1760 to 1956 KWH.

Exhibit 8-4 In Order to Estimate the Average Electric Usage Per Month,a