Feeling sleepy? The first four students to arrive for a first-period statistics class were asked how much sleep (to the nearest hour) they got last night. Their responses were 7, 7, 9, and 9.

(a) Find the standard deviation from its definition. That is, find the deviations of each observation from the mean, square the deviations, then obtain the variance and the standard deviation.

(b) Interpret the value of sx you obtained in part (a).

(c) Do you think it’s safe to conclude that the mean amount of sleep for all 30 students in this class is close to 8 hours? Why or why not?