Question

Let x₁ , x₂ , ...., xⁿ be n observations such that ∑x₁² = 400 and ∑x_i = 80. Then a possible value of n among the following is

(a) 18 

(b) 15

(c) 12 

(d) 9.

Answer 1

(a) : Using well known fact that root mean square of number ≥ A.M. of the numbers

=> n = 17 but not given in choice.
∴ n = 18 is correct number.