Students at a major university are complaining of a serious housing crunch. Many of the university's students, they complain, have to commute too far to school because there is not enough housing near campus. The university officials respond with the following information: the mean distance commuted to school by students is 16.0 miles.

Assuming that the university officials' information is correct, complete the following statements about the distribution of commute distances for students at this university.

(a) According to Chebyshev's theorem, at least of the commute distances lie within 2 standard deviations of the mean, 16.0 miles.

(b) Suppose that the distribution is bell-shaped. If approximately 68% of the commute distances lie between 12.3 miles and 19.7 miles, then the approximate value of the standard deviation of the distribution, according to the empirical rule, is____.

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