Among the 10 known data, the average and variance of the first nine data are 1 and 7, respectively The 10th data is equal to 11, so what is the variance of the 10th data?

Among the 10 known data, the average and variance of the first nine data are 1 and 7, respectively The 10th data is equal to 11, so what is the variance of the 10th data?

Let 10 digits be a, b... I, J, then the 10th digit J = 11, the average of these 10 digits is (9 * 1 + 11) / 10 = 2, the variance is 1 / 10 * [(A-2) ^ 2 +... + (I-2) ^ 2 + (J-2) ^ 2], the variance of the first nine digits is 1 / 9 * [(A-1) ^ 2 +... (i-1) ^ 2] = 7, there is (A-1) ^ 2 +... (i-1) ^ 2 = 63 --- 1 formula (A-2) ^ 2 +... (I-2) ^ 2