var avg = nums.Average();
            //总体方差
            var variance = nums.Sum(x => Math.Pow(x - avg, 2))/nums.Count();
            //样本方差
            var sampleVariance=  nums.Sum(x => Math.Pow(x - avg, 2)) / (nums.Count()-1);

            //总体标准差
            var standDeviation = Math.Sqrt(variance);

            //样本标准差
            var sampleDeviation = Math.Sqrt(sampleVariance);