Do you remember in Chapter 2, *The Shape of Data*, when we described the normal distribution and how ubiquitous it is? The behavior of many random variables in real life is very well described by a normal distribution with certain parameters.

The two parameters that uniquely specify a normal distribution are *µ* (*mu*) and *σ* (*sigma*). *µ*, the mean, describes where the distribution's peak is located and *σ*, the standard deviation, describes how wide or narrow the distribution is.

Figure 4.3: Normal distributions with different parameters

The distribution of heights of American females is approximately normally distributed with ...