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public static double WeightedAverage<T>(this IEnumerable<T> records, Func<T, double> value, Func<T, double> weight)
    {
        double weightedValueSum = records.Sum(x => value(x) * weight(x));
        double weightSum = records.Sum(x => weight(x));

        if (weightSum != 0)
            return weightedValueSum / weightSum;
        else
            throw new DivideByZeroException("Your message here");
    }