# Weighted arithmetic mean

Weighted arithmetic mean means the arithmetic mean of sample results weighted by the number of subsamples in each sample. Its purpose is to give influence to a sample relative to the surface area it represents. A single surface sample is comprised of a single subsample. A composite sample may contain from two to four subsamples of the same area as each other and of each single surface sample in the composite. The weighted arithmetic mean is obtained by summing, for all samples, the product of the sample's result multiplied by the number of subsamples in the sample, and dividing the sum by the total number of subsamples contained in all samples. For example, the weighted arithmetic mean of a single surface sample containing 60 g/ft 2, a composite sample (three subsamples) containing 100 g/ft 2, and a composite sample (4 subsamples) containing 110 g/ft 2 is 100 g/ft 2. This result is based on the equation [60 + (3*100) + (4*110)]/(1 + 3 + 4).

40 CFR § 745.63

## Scoping language

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