Question

Let S_n = Σ (- 1) ⁱ⁺¹ i,  i ∈[i=1,n] then S₁₀₁ equals

(A) 48 

(B) 49 

(C) 50 

(D) 51

Answer 1

Correct Answer is: (D) 51

S₁₀₁ = (1–2) + (3 – 4) + ... + (99 – 100) + 101

= (– 1) × 50 + 101 = 51