In mathematics and statistics, the arithmetic mean is the sum of a collection of numbers divided by the count of numbers in the collection.
$$\bar{a}=\frac{a_{1}+a_{2}+...+a_{n}}{n}=\frac{1}{n} \times \sum_{i=1}^{n}a_{i}$$
where,
a1, ...— data set;
n— number of values.
$$\bar{a}=\frac{a_{1}\times b_{1}+...+a_{n} \times b_{n}}{b_{1}+...+b_{n}}=\frac{\sum_{i=1}^{n}a_{i} \times b_{i}}{\sum_{i=1}^{n}b_{i}} $$
where,
b1, ...— non-negative weights.