It is given that sum of the first (x−1) numbers is equal to sum of the numbers from (x+1) to 49 or, sum of (x−1) numbers = sum of first 49 numbers - sum of first numbers
x(x−1)
2
=
49×50
2
−
x(x+1)
2
On solving, we get x=35 Hence, option C is the correct answer.