For the next 3 questions, please read the description below.Researchers want to estimate the mean monthly electricity bill in alarge urban area using a simple random sample of 100 households.Their calculation shows that the sample standard deviation is$15.50.
*Assume that the population standard deviation is unknown.Whatis the error of estimate for a 99% confidence interval?
answer choices 3.67 4.07 3.99 4.73
*Assume that the population standard deviation is known to be$30. The average monthly electricity bill of the 100 households is$120. What is the upper bound for a 90% confidence interval?
answer choices 124 122 125 123
*Assume that the population standard deviation is unknown. Ifthe researchers want to decrease the error of estimate, which ofthe following number of households is more likely to be theirsample size?
answer choices 30 100 90 120
