A class survey in a large class for first year college students asked, "About how many minutes ...

     A class   survey in a large class for first year college students asked, "About   how many minutes do you study on a typical weeknight?"  The   mean response of the 269 students was x (bar over the x) = 137   minutes.  Suppose that we know that the study time follows a Normal   distribution with standard deviation = 65 minutes in the population of all   first year students at this university.      A) Use the survey result to   give a 99% confidence interval for the mean study time of all first year   students.       B)  What condition   not yet mentioned must be met for confidence interval to be valid?