Question

In an A.P, the first term is 25, nth term is -17 and the sum of n terms is 132. Find n and the common difference.

Answer 1

First-term a = 25

nth term = -17 => last term l = -17

Sum of n terms = 132

`=> n/2 [a + l] = 132`

=> n(25 - 17) = 264

`=> n xx 8 = 264`

`=> n = 33`

Now l = -17

`=> a + (n - 1)d = -17`

`=> 25 + 32d = -17`

=> 32d = -42

`=> d = -42/32`

`=> d = -21/16`