Astudy has indicated that the sample size necessary to estimate the average electricity use by residential customers of a large western utility company is 900 customers. assuming that the margin of error associated with the estimate will be ± 20 watts and the confidence level is stated to be 95 percent, what was the value for the population standard deviation? possible answers =
a. approximately 68.5
b. about 306.122
c. about 13.2
d. around 425.3