N8

1. For a sample 1000 Twitter users, Elon Musk's research department reports an average age of 39. If the population standard deviation is 9.5 years, what would be the upper bound for a 90% confidence interval estimate of the mean age of all Twitter users?

2. The average annual health care cost in a random sample of 600 U.S. adults is $8562. If the standard deviation for health care costs in the population is $1230, compute the margin of error in a 90% confidence interval estimate of the mean annual health care cost for all U.S. adults.