In Order to Estimate the Average Electric Usage Per Month

Multiple Choice

In order to estimate the average electric usage per month, a sample of 64 houses was selected and the electric usage was determined. Assume a population standard deviation of 320 kilowatt-hours. If the sample mean is 1858 kWh, the 95% confidence interval estimate of the population mean is _____ kWh.

A) 1779.6 to 1936.4
B) 1818 to 1898
C) 1792.2 to 1923.8
D) 1538 to 2178