Question

In an A.P. , the first term is 25, nth term is -17 and the sum of first nth term is 60 find the common difference

Answer 1

Sn=60
60=n/2(25-17)
120=8n
n=15
An=-17
-17=25+(14)d
-42=14d
d=-3

Answer 2

Hi,
Given, a = 25, An = -17, Sn = 60 , d=?
First we'll find the value of n.

Sn = n/2 (a+An)
60 = n/2 (25-17)
120 = 8n
n = 120/8 = 15

Now,
An = a+(n-1)d
An = a+(15-1)d
An = a+(14)d
-17 = 25+14d
14d = -42
d = -3

Cheers!