Weighted mean
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Given a set of data, X={x₁, x₂, ..., x_n} and corresponding weights, W={w₁, w₂, ..., w_n} the weighted mean is calculated as

Note that if all the weights are equal, the weighted mean is the same as the arithmetic mean.

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See also: average

The original article can be found at: http://en.wikipedia.org/wiki/Weighted_mean.
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