Find the number of terms in each of the following APs :

18, 15, 13 …. , -47

Given first term (a) = 18

Common difference (d) = n₂-n₁ = 15 - 18 = 2.5

a_n = -47

⇒ a_n = a + (n-1)d

-47 = 18 +(n-1) 2.5

65 = (n-1) 2.5

(n-1) = 26

n = 27

Therefore -47 is 27^th term of the series