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# CEE 110 Introduction to Probability and Statistics (problem 4-82 in text)

Phoenix water is provided to approximately 1.4 million people, who are served through more than 362,000 accounts (http://phoenix.gov/WATER/wtrfacts.html). All accounts are metered and billed monthly. The probability that an account has an error in a month is 0.001; accounts can be assumed to be independent.

Assume that results between months are independent.

[362, 19.0, 0.256, 392.3, 4.62×10-4]

- What is the mean and standard deviation of the number of account errors each month?
- Approximate the probability of fewer than 350 errors in a month.
- Approximate a value so that the probability that the number of errors exceeding this value is 0.05.
- Approximate the probability of more than 400 errors per month in the next two months.

Assume that results between months are independent.

[362, 19.0, 0.256, 392.3, 4.62×10-4]

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