read mean document
$$ \begin{equation*} \text{Sum of all elements} = X_1 + X_2 + X_3 + X_4 + X_5 + . . . + X_n \end{equation*}
$$ $$ \begin{equation*} X_1 + X_2 + X_3 + X_4 + X_5 + . . . + X_n = \sum\limits_{i=1}^{n} X_i \end{equation*}
$$ $$ \begin{equation*} \frac{\sum\limits_{i=1}^{n} X_i}{n} \end{equation*}
$$ $$ \begin{equation*} \mu = \frac{\sum\limits_{i=1}^{n} X_i}{n} \end{equation*}
$$ |age | 19 | 20 | 21 | |freq | 1 | 3 | 1 | $$ \begin{equation*} \begin{split} \mu = \frac{\sum\limits_{}^{} \text{fx}}{\sum{\text{f}}} = \frac{1 \text{x} 19 + 3 \text{x} 20 + 1 \text{x} 21}{5} \end{split} \end{equation*}
$$

see median document

{19, 19, 20, 20, 20, 21, 21, 100, 102}

{19, 20, 20, 20, 21, 21, 100, 102}

e.g.,

1. Get mean, median for each data set.
2. State how each is skewed.

{1, 1, 1, 2, 2, 2, 2, 3, 3, 31, 31, 32, 32, 32, 32, 33, 33, 33}

{1, 1, 1, 2, 2, 2, 2, 2, 3, 3, 31, 31, 32, 32, 32, 32, 33, 33, 33}

{1, 1, 1, 2, 2, 2, 2, 2, 3, 31, 31, 31, 32, 32, 32, 32, 33, 33, 33}

see mode document

modality
bimodal
trimodal
multimodal
unimodal

It works for both number measured and category measured data.