20. A teacher wants to know how well her students performed on the first exam. First calculate the mean, SS and standard deviation (SD) of the sample of test scores below. (Show your work!) Then use the M and SD to find the values that define or separate the middle 68% of scores. Hint: remember the empirical rule. In other words, report this: a. M = b. SS = c. SD = d. On this exam 68% of students scored between and on the exam. Exam 1 scores: 92, 80, 73, 94, 89, 79, 51, 98