The sum of the even numbers between 1 and k is 79*80, where k is an odd number, then k=?

(A) 79

(B) 80

(C) 81

(D) 157

(E) 159

Detailed Answers

(E) 159

sum of numbers till n = n(n+1)/2 , sum of even numbers will be almost half of this i.e. n(n+1)/4 .

so if S = 79.80, then n= 159.