Let the Mean and Standard Deviation of Marks of Class A of 100 Students Be 40 and α, and of Class B of n Students Be 55 and 30 − α. If the Mean and Variance of the Combined Class of 100 + n Students Are 50 and 350, Then the Sum of Variances of Classes A and B Is
Class A (100 students, mean 40, SD α) and Class B (n students, mean 55, SD 30−α) combine to mean 50, variance 350. Find the sum of variances of A and B.