2.109 What does s equal?

a. For an exam given to a class, the students’ scores ranged from 35 to 98, with a mean of 74. Which of the following is the most realistic value for the standard deviation: -10, 1, 12, 60? Clearly explain what is unrealistic about the other values.

b. The sample mean for a data set equals 80. Which of the following is an impossible value for the standard deviation? 200, 0, -20? Why?