Given: The sequence is 25, 22, 19,...... and the sum of certain number of terms of this sequence is 115 Let there n be term of the given sequence such that Sn=115 Here, a = 25, d = - 3 As we know that, Sn=
n
2
×[2a+(n−1)d] ⇒Sn=
n
2
×[2.(25)+(n−1)(−3)]=115 ⇒3n2−53n+230=0 ⇒n=10 or 23∕3 but ∵n is natural number ⇒n=10 As we know that,Sn=