Question

The electric cooperative needs to know the mean household usage of electricity by its non-commercial customers in kWh per day. They would like the estimate to have a maximum error of 0.12 kWh. A previous study found that for an average family the variance is 1.96 kWh and the mean is 15.1 kWh per day. If they are using a 95% level of confidence, how large of a sample is required to estimate the mean usage of electricity? Round your answer up to the next integer.

Answer 1

Solution :

Z/2 = Z0.025 = 1.96  

sample size = n = [Z/2* / E] 2

n = [ 1.96 * 1.4 / 0.12]2

n = 522.88

Sample size = n = 523