For an A.P. the sum of its terms is 60, common difference is 2 and last term is 18. Find the number of terms in the A.P.

Given, Common difference (d) = 2 Last term (l) = 18 Let no. of terms be n. ⇒ l = a + (n - 1)d ⇒ 18 = a + 2(n - 1) ⇒ 18 = a + 2n - 2 ⇒ a + 2n = 20 ⇒ a = 20 - 2n .........(1) By formula, S n = Substituting values we get : Substituting value of a in above equation, we get : Hence, no. of terms = 4 or 15.