Arithmetic progression

In a Society, the houses are arranged in one line numbering 1 to 49. What is that value of 'x' for which the sum of the numbers of the houses preceding the house number 'x' is equal to the sum of the numbers of the houses following it.

Answer:

X (X - 1)/2 = 49 x 50/2 - X (X + 1)/2

Or, X² = 1225

Or, X = 35