九、乳酸菌粉的重量資料如下，請計算這 20 包乳酸菌粉重量的變異數。18, 17, 18, 16, 17, 15, 15, 16, 18, 15, 14, 16, 12, 14, 13, 16, 15, 19, 16, 16