Question

PLEASE SOLVE ITS A BOARD QUESTION 2016 CLASS 10

Answer 1

Answer:

35

Step-by-step explanation:

Let s(n) be the sum of first n houses , s(n-1) be the sum of first (n-1) houses , and s(49) be the sum of 49 houses .

Now s(n-1) = s(49) - s(n) …1

GENERAL FORMULA FOR SUM OF N TERMS OF AN AP :

Let us use the second formula for the sum . Note : a(1) is nothing but the first term of the AP which in this problem is 1

s(n-1) = (n)/2 [2*a(1) + (n–1)*d] = (n-1)/2 [n]

s(49) = (49–1)/2 [2 + 48] = 48/2 * 50 = 1200

s(n) = (n)/2 [2 + (n–1)] = n/2 [1+n]

From …1

(n-1)/2 [n] = 1200 + n/2 [1+n]

=> n = 35