ExplanationDraw two bell curves: one for rural areas, and one for urban areas. The three standard deviations above the mean each represent 34%, 14% and 2% of the population, respectively.
The mean in both cases is 8. In rural areas, 2% of the citizens take more than 12 holidays a year, so 12 is two standard deviations above 8; the standard deviation is thus the difference between 8 and 12 divided by 2, or 2. In urban areas, similarly, the standard deviation is 16 – 8 divided by 2, or 4.
The difference between the two standard deviations is thus 4 – 2 = 2.
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