[3.8] bpo-36546: Add examples to elucidate the formulas (GH-14898)

Doc/library/statistics.rst

@@ -527,14 +527,18 @@ However, for reading convenience, most of the examples show sorted sequences.
    The default *method* is "exclusive" and is used for data sampled from
    a population that can have more extreme values than found in the
    samples.  The portion of the population falling below the *i-th* of
-   *m* data points is computed as ``i / (m + 1)``.
+   *m* sorted data points is computed as ``i / (m + 1)``.  Given nine
+   sample values, the method sorts them and assigns the following
+   percentiles: 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%.
 
    Setting the *method* to "inclusive" is used for describing population
-   data or for samples that include the extreme points.  The minimum
-   value in *dist* is treated as the 0th percentile and the maximum
-   value is treated as the 100th percentile.  The portion of the
-   population falling below the *i-th* of *m* data points is computed as
-   ``(i - 1) / (m - 1)``.
+   data or for samples that are known to include the most extreme values
+   from the population.  The minimum value in *dist* is treated as the 0th
+   percentile and the maximum value is treated as the 100th percentile.
+   The portion of the population falling below the *i-th* of *m* sorted
+   data points is computed as ``(i - 1) / (m - 1)``.  Given 11 sample
+   values, the method sorts them and assigns the following percentiles:
+   0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%.
 
    If *dist* is an instance of a class that defines an
    :meth:`~inv_cdf` method, setting *method* has no effect.