6.3 Working with Normally Distributed Variables
As illustrated in the previous example, the 68.26-95.44-99.74 rule allows us to obtain useful information about a normally distributed variable quickly and easily
Experience has shown that the 68.26-95.44-99.74 rule works reasonably well for any variable having approximately a bell-shaped distribution, regardless of whether the variable is normally distributed. This fact is referred to as the empirical rule,该法则适用于形状似钟的分布，有时可能该分布不是正态分布。
1.可以通过概率找z-score
2.可以通过z-score找概率
