The author surveyed one of his statistics classes. The numbers of units (hours or credits) students were enrolled in are shown in Table 28.

a. Construct a histogram. Begin with lower class limit 4 units and class width 2 units. Describe the shape of the distribution. Can the Empirical Rule be applied?
b. Compute the mean and standard deviation.
c. According to the Empirical Rule, approximately what percentage of the observations should lie within one standard deviation of the mean?
d. Count the actual number of observations shown in Table 28 that lie within one standard deviation of the mean. What percentage is that of the 42 students? Compare the percentage with the result you found in part (c).
e. A student concludes that the mean and the standard deviation you found in part (b) describe the center and the spread of the numbers of units for all students enrolled at the college. What would you tell the student?

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Table 28 Numbers of Units 16 10 1 13 13 15 15 13 15 17 13 17 13 14 11 14 12 14 14 16 12 15 11 13 10 13 10 15 15 16 8 13 16 14 12.5 14 18 4 13 11 13 5