Assume that the daily screen time of smart phone for college students follows normal distribution (with the standard deviation is unknown). 5 students are randomly selected, and their daily screen time (in hours) are as follows: (12 marks)

6, 7, 8, 8, 11

a. Find the mode, median, sample mean and sample standard deviation for this sample. (5 marks)

b. At the significance level of 5%, do the data provide sufficient evidence to conclude that the average daily screen time of smart phone for college students is more than 6 hours. (7 marks)