6 19 Student study times A class survey in a large class for first year college students asked About how many hours do you study during a typical week The mean response of the 463 students was as x 13 7 hours 6 Sup pose that we know that the study time follows a Normal distribution with standard deviation o 7 4 hours in mobo the population of all first year students at this university boird a Use the survey result to give a 99 confidence inter val for the mean study time of all first year students b What condition not yet mentioned must be met for onfidence interval to be valid