1) A survey taken in 2010 polled 100 randomly chosen cell phone users. They answered the question: "What is your average monthly cell phone bill?" The following are the characteristics of the sample: The sample mean is $80. Assume the population standard deviation to be $20. Give a 90% confidence interval for the mean monthly cell phone bill. a) (76.71,83.29) b) (80.00,82.56) c) (78.00,82.00) d) (77.73,81,27) e) None of the above