Question

First and last term of A.P. are 2 and 34 respectively.  Sum of its terms is 90 then value of n will be :

(A) 3

(B) 4

(C) 5

(D) 6

Answer 1

Answer is (C) 5

We have a = 2, l = 34, d = 8, S_n = 90

⇒ S_n = n/2(a + l)

⇒ 90 = n/2(a + l)

⇒ n/2 × 36 = 90

⇒ n × 18 = 90

⇒ n = 90/18 = 5

⇒ n = 5