In order to estimate the average electric usage per month, a sample of 64houses was selected and the electric usage was determined. Assume a population standard deviation of 320 kilowatt-hours. At 95% confidence, the size of the margin of error is
A) 1.96.
B) 40.00.
C) 78.40.
D) 65.80.

Question

Quizplus · Accepted Answer

The formula to calculate the margin of error is:

Margin of Error = Z* * (standard deviation / sqrt(sample size))

Where Z* is the critical value of the standard normal distribution at the desired confidence level.

At 95% confidence level, Z* = 1.96.

Plugging in the given values:

Margin of Error = 1.96 * (320 / sqrt(64))
Margin of Error = 78.4

Therefore, the size of the margin of error is 78.4 kilowatt-hours, which is option C.

In Order to Estimate the Average Electric Usage Per Month