According to Nielsen Media Research, the average number of hours of TV viewing per household per week in the United States is 50.4 hours. Suppose the standard deviation is 10.6 hours and a random sample of 49 U.S. households is taken.
C) What is the probability that the sample average is less than 39 hours?
D) Suppose the population standard deviation is unknown. If 71% of all sample means are greater than 49 hours and the population mean is still 50.4 hours, what is the value of the population standard deviation?