3 For many random variables, a good choice is the normal distribution, often represented as a bell-shaped curve, shown in Figure 1.

3对于许多随机变量来说，一个好的选择是正态分布，常常表现为一个钟型曲线，如图1所示。

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However, for symmetrical, bell shaped distribution, we can be more precise in explaining the dispersion about the mean.

然而，为对称的钟形分布，我们可以更精确地解释有关平均值的分散。

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Imagine a society that has a bell-shaped income distribution curve with a broad middle class, a smaller number of rich and poor, and an even smaller number of super rich and super poor.

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