Between what two values would be considered a normal bill? Remember, being within 2 Standard Deviations is considered normal.

Log onto website where you can observe your service bill for the last 12 months (electric bill, cell phone bill, water bill, etc.). If you do NOT feel comfortable sharing this data, you can make up values.

In excel, list the values of your bill for the last 12 months on one column.
Find the sample mean and sample standard deviation of your data.
Pick three bills from the last 12 months and change the values into z-scores. What does the z-score tell you about that particular month?

Analysis

Between what two values would be considered a normal bill? Remember, being within 2 Standard Deviations is considered normal.
Are any of your bills in the last 12 months unusual? Very unusual?
Are there times when you would accept an “unusual” bill? Explain.