QUESTION 1 ( KNOWN): An article in the National Geographic News argues that Americans are increasingly skimping on their sleep. A researcher in a small Midwestern town wants to estimate the mean weekday sleep time of its adult residents. He takes a random sample of 80 adult residents and records their weekday mean sleep time as 6.4 hours. Assume that the population standard deviation is fairly stable at 1.8 hours.

a. What is the point estimate of the population mean?

b. At 95% confidence, what is the margin of error?

c. Calculate the 95% confidence interval for the population mean weekday sleep time of all adult residents of this Midwestern town.

QUESTION 2 ( UNKNOWN): Students who graduated from college in 2010 owed an average of $25,250 in student loans. An economist wants to determine if average debt has changed. She takes a sample of 40 recent graduates and finds that their average debt was $27,500 with a standard deviation of $9,120.

a. Calculate the margin of error with 90% confidence.

Your answer

b. Construct the 90% confidence interval.