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 two standard deviations of the mean?
d. Count the actual number of observations shown in Table 28 that lie within two standard deviations of the mean. What percentage is that of the 42 students? Compare the percentage with the result you found in part (c).

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Table 28 Numbers of Units 16 10 11 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