Question

Let in a series of 2n observations, half of them are equal to a and remaining half are equal to –a. Also by adding a constant b in each of these observations, the mean and standard deviation of new set become 5 and 20, respectively. Then the value of a² + b² is equal to :

(1) 425

(2) 650

(3) 250

(4) 925 

Answer 1

Correct option is (1) 425

Let observations are denoted by x_i for 1 ≤ i < 2n