Final answer:
Approximately 95% of the data is within two standard deviations from the mean for a bell-shaped distribution; hence, the percentage of roadways with potholes between 39 and 71 is about 95%.
Step-by-step explanation:
Using the empirical rule for a bell-shaped distribution, we can determine the percentage of 1-mile long roadways with potholes numbering between 39 and 71. The rule states that approximately 68% of the data falls within one standard deviation (±1 SD), 95% within two standard deviations (±2 SD), and 99.7% within three standard deviations (±3 SD) from the mean. Since one standard deviation from the mean is 63 ± 8, this does not cover our range. However, two standard deviations from the mean, which is the range from 63 - 2(8) = 47 to 63 + 2(8) = 79, does fully cover our range of interest from 39 to 71. Therefore, we are interested in the percentage within two standard deviations from the mean, which is approximately 95%.