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. if the sample mean is 1858 kwh, the 95% confidence interval estimate of the population mean is

The 95% confidence interval estimate of the population mean is (1760, 1956) .

Step-by-step explanation:

Formula for confidence interval for population mean() :

, where n= Sample size

= sample mean.

= Two-tailed critical z-value

= population standard deviation.

By considering the given information, we have

n= 81

kilowatt-hours.

kilowatt-hours.

By using the z-value table ,

The critical values for 95% confidence interval :

Now , the 95% confidence interval estimate of the population mean will be :

Hence, the 95% confidence interval estimate of the population mean is (1760, 1956) .

r and t.

both are 64 degrees.