Arithmetic Mean (AM)

Arithmetic mean is computed as the sum of all the numbers in the series divided by the count of all numbers in the series. Commonly referred to as "average" or simply as "mean".

AM = (X₁ + X₂ + … + X_n) / n

The sum of the deviations is zero, Σ(X_i-X_a)=0, where X_a is the average (i.e. mean)

Population mean
u= (ΣX_i) / n

Sample mean
Xs = (ΣX_i) / (n)

Weighted mean (WM) or weighted average
Take the corresponding weights into account. For equal weights, the weighted mean equals the arithmetic mean.

WM= (w₁X₁ + w₂X₂ + … + w_nX_n) / (w₁ + w₂ + … + w_n)

X_w = ( ΣX_iW_i) / (ΣW_i)