Question

The first and the last term of an A.P are -4 and 146 and the sum of the A.P is 7171. Find the number of terms in the A.P and the A.P.

Answer 1

Given a = -4, l = 146.

We have l = a + (n – 1)d = 146 = -4 + (n – 1)d

⇒ (n – 1)d = 150

Also we have Sn = n/2{2a + (n – 1)d}

7171 = n/2{2(-4) + 150}

14342 = n{-8 + 150}

⇒ 142n = 14342

∴ n = 14342/142 = 101

So number of terms is A.P = 101

consider (n – 1)d = 150.

⇒ (101 - 1)d = 150

d = 150/100 = 1.5