Agroup of statistics students decided to conduct a survey at their university to find the average (mean) amount of time students spent studying per week. they sampled 240 students and found a mean of 22.3 hours per week. assuming a population standard deviation of six hours, what is the confidence interval at the 95% level of confidence? ( use student's t distribution (appendix b.5) at infinite degrees of freedom for three decimal accuracy of the required z value.)