3. As an engineer working for an electrical power company you need to design an

Question

3. As an engineer working for an electrical power company you need to design an experiment to determine a 95% confidence interval for the mean daily power usage for homes in Salt Lake City. Measuring the daily power usage of every single home is not practical; therefore you need to choose a sample. What size does your sample need to be to ensure that the confidence interval for is not larger than ±5kWh? Or in other words, what is the minimum sample size that can be used to be 95% confident that the error between the sample mean X and the population mean u will not exceed 5 kWh? Assume that the standard deviation for the population distribution of power usage is known to be 50kW h.

Explanation / Answer

3)

for 95 % CI value of z= 1.9600 standard deviation = 50 margin of error E = 5 required sample size n=(z/E)2                                        = 385

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