Question

Use this information for the next few questions. The electric company just sent you a letter with your average daily electricity usage over the entire time you have lived in your house (several years). Daily usage is normally distributed with the average of 18 kilowatt-hours and a standard deviation of 4 kilowatthours. You are also interested in your average cost of electricity over month-long periods (30 days). When you draw the normal distribution for daily usage and label the mean plus or minus two SDs, what numbers do you get across the bottom of the x-axis?

1. 14,16,18,20,22
2. 16,17,18,19,20
3. 2,10,18,26,34
4. 10,14,18,22,26

Answer 1

The numbers across the bottom of the x-axis representing the mean plus or minus two standard deviations from the mean daily electricity usage of 18 kWh with a standard deviation of 4 kWh would be 10, 14, 18, 22, and 26.

Step-by-step explanation:

When drawing the normal distribution for daily electricity usage with an average (mean) of 18 kilowatt-hours and a standard deviation of 4 kilowatt-hours, and labeling the mean plus or minus two standard deviations, we plot points on the x-axis that represent the average plus two standard deviations and the average minus two standard deviations. In this case, two standard deviations above and below the mean are:

• 18 + 2(4) = 26
• 18 - 2(4) = 10

So, the numbers across the bottom of the x-axis would be 10, 14, 18, 22, and 26, which correspond to the mean (18) minus two standard deviations, minus one, the mean, plus one, and plus two standard deviations.